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my lastIndexOf is not working in my project [duplicate]

I've got an array:
myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}, etc.]
I'm unable to change the structure of the array. I'm being passed an id of 45, and I want to get 'bar' for that object in the array.
How do I do this in JavaScript or using jQuery?

Use the find() method:
myArray.find(x => x.id === '45').foo;
From MDN:
The find() method returns the first value in the array, if an element in the array satisfies the provided testing function. Otherwise undefined is returned.
If you want to find its index instead, use findIndex():
myArray.findIndex(x => x.id === '45');
From MDN:
The findIndex() method returns the index of the first element in the array that satisfies the provided testing function. Otherwise -1 is returned.
If you want to get an array of matching elements, use the filter() method instead:
myArray.filter(x => x.id === '45');
This will return an array of objects. If you want to get an array of foo properties, you can do this with the map() method:
myArray.filter(x => x.id === '45').map(x => x.foo);
Side note: methods like find() or filter(), and arrow functions are not supported by older browsers (like IE), so if you want to support these browsers, you should transpile your code using Babel (with the polyfill).

As you are already using jQuery, you can use the grep function which is intended for searching an array:
var result = $.grep(myArray, function(e){ return e.id == id; });
The result is an array with the items found. If you know that the object is always there and that it only occurs once, you can just use result[0].foo to get the value. Otherwise you should check the length of the resulting array. Example:
if (result.length === 0) {
// no result found
} else if (result.length === 1) {
// property found, access the foo property using result[0].foo
} else {
// multiple items found
}

Another solution is to create a lookup object:
var lookup = {};
for (var i = 0, len = array.length; i < len; i++) {
lookup[array[i].id] = array[i];
}
... now you can use lookup[id]...
This is especially interesting if you need to do many lookups.
This won't need much more memory since the IDs and objects will be shared.

ECMAScript 2015 (JavaScript ES6) provides the find()
method on arrays:
var myArray = [
{id:1, name:"bob"},
{id:2, name:"dan"},
{id:3, name:"barb"},
]
// grab the Array item which matchs the id "2"
var item = myArray.find(item => item.id === 2);
// print
console.log(item.name);
It works without external libraries. But if you want older browser support you might want to include this polyfill.

Underscore.js has a nice method for that:
myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'},etc.]
obj = _.find(myArray, function(obj) { return obj.id == '45' })

I think the easiest way would be the following, but it won't work on Internet Explorer 8 (or earlier):
var result = myArray.filter(function(v) {
return v.id === '45'; // Filter out the appropriate one
})[0].foo; // Get result and access the foo property

Try the following
function findById(source, id) {
for (var i = 0; i < source.length; i++) {
if (source[i].id === id) {
return source[i];
}
}
throw "Couldn't find object with id: " + id;
}

myArray.filter(function(a){ return a.id == some_id_you_want })[0]

A generic and more flexible version of the findById function above:
// array = [{key:value},{key:value}]
function objectFindByKey(array, key, value) {
for (var i = 0; i < array.length; i++) {
if (array[i][key] === value) {
return array[i];
}
}
return null;
}
var array = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
var result_obj = objectFindByKey(array, 'id', '45');

Performance
Today 2020.06.20 I perform test on MacOs High Sierra on Chrome 81.0, Firefox 77.0 and Safari 13.1 for chosen solutions.
Conclusions for solutions which use precalculations
Solutions with precalculations (K,L) are (much much) faster than other solutions and will not be compared with them - probably they are use some special build-in browser optimisations
surprisingly on Chrome and Safari solution based on Map (K) are much faster than solution based on object {} (L)
surprisingly on Safari for small arrays solution based on object {} (L) is slower than traditional for (E)
surprisingly on Firefox for small arrays solution based on Map (K) is slower than traditional for (E)
Conclusions when searched objects ALWAYS exists
solution which use traditional for (E) is fastest for small arrays and fast for big arrays
solution using cache (J) is fastest for big arrays - surprisingly for small arrays is medium fast
solutions based on find (A) and findIndex (B) are fast for small arras and medium fast on big arrays
solution based on $.map (H) is slowest on small arrays
solution based on reduce (D) is slowest on big arrays
Conclusions when searched objects NEVER exists
solution based on traditional for (E) is fastest on small and big arrays (except Chrome-small arrays where it is second fast)
solution based on reduce (D) is slowest on big arrays
solution which use cache (J) is medium fast but can be speed up if we save in cache also keys which have null values (which was not done here because we want to avoid unlimited memory consumption in cache in case when many not existing keys will be searched)
Details
For solutions
without precalculations: A
B
C
D
E
F
G
H
I
J (the J solution use 'inner' cache and it speed depend on how often searched elements will repeat)
with precalculations
K
L
I perform four tests. In tests I want to find 5 objects in 10 loop iterations (the objects ID not change during iterations) - so I call tested method 50 times but only first 5 times have unique id values:
small array (10 elements) and searched object ALWAYS exists - you can perform it HERE
big array (10k elements) and searched object ALWAYS exist - you can perform it HERE
small array (10 elements) and searched object NEVER exists - you can perform it HERE
big array (10k elements) and searched object NEVER exists - you can perform it HERE
Tested codes are presented below
function A(arr, id) {
return arr.find(o=> o.id==id);
}
function B(arr, id) {
let idx= arr.findIndex(o=> o.id==id);
return arr[idx];
}
function C(arr, id) {
return arr.filter(o=> o.id==id)[0];
}
function D(arr, id) {
return arr.reduce((a, b) => (a.id==id && a) || (b.id == id && b));
}
function E(arr, id) {
for (var i = 0; i < arr.length; i++) if (arr[i].id==id) return arr[i];
return null;
}
function F(arr, id) {
var retObj ={};
$.each(arr, (index, obj) => {
if (obj.id == id) {
retObj = obj;
return false;
}
});
return retObj;
}
function G(arr, id) {
return $.grep(arr, e=> e.id == id )[0];
}
function H(arr, id) {
return $.map(myArray, function(val) {
return val.id == id ? val : null;
})[0];
}
function I(arr, id) {
return _.find(arr, o => o.id==id);
}
let J = (()=>{
let cache = new Map();
return function J(arr,id,el=null) {
return cache.get(id) || (el=arr.find(o=> o.id==id), cache.set(id,el), el);
}
})();
function K(arr, id) {
return mapK.get(id)
}
function L(arr, id) {
return mapL[id];
}
// -------------
// TEST
// -------------
console.log('Find id=5');
myArray = [...Array(10)].map((x,i)=> ({'id':`${i}`, 'foo':`bar_${i}`}));
const mapK = new Map( myArray.map(el => [el.id, el]) );
const mapL = {}; myArray.forEach(el => mapL[el.id]=el);
[A,B,C,D,E,F,G,H,I,J,K,L].forEach(f=> console.log(`${f.name}: ${JSON.stringify(f(myArray, '5'))}`));
console.log('Whole array',JSON.stringify(myArray));
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.min.js"></script>
This snippet only presents tested codes
Example tests results for Chrome for small array where searched objects always exists

As others have pointed out, .find() is the way to go when looking for one object within your array. However, if your object cannot be found using this method, your program will crash:
const myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
const res = myArray.find(x => x.id === '100').foo; // Uh oh!
/*
Error:
"Uncaught TypeError: Cannot read property 'foo' of undefined"
or in newer chrome versions:
Uncaught TypeError: Cannot read properties of undefined (reading 'foo')
*/
This can be fixed by checking whether the result of .find() is defined before using .foo on it. Modern JS allows us to do this easily with optional chaining, returning undefined if the object cannot be found, rather than crashing your code:
const myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
const res = myArray.find(x => x.id === '100')?.foo; // No error!
console.log(res); // undefined when the object cannot be found

If you do this multiple times, you may set up a Map (ES6):
const map = new Map( myArray.map(el => [el.id, el]) );
Then you can simply do a O(1) lookup:
map.get(27).foo

You can get this easily using the map() function:
myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
var found = $.map(myArray, function(val) {
return val.id == 45 ? val.foo : null;
});
//found[0] == "bar";
Working example: http://jsfiddle.net/hunter/Pxaua/

Using native Array.reduce
var array = [ {'id':'73' ,'foo':'bar'} , {'id':'45' ,'foo':'bar'} , ];
var id = 73;
var found = array.reduce(function(a, b){
return (a.id==id && a) || (b.id == id && b)
});
returns the object element if found, otherwise false

You can use filters,
function getById(id, myArray) {
return myArray.filter(function(obj) {
if(obj.id == id) {
return obj
}
})[0]
}
get_my_obj = getById(73, myArray);

While there are many correct answers here, many of them do not address the fact that this is an unnecessarily expensive operation if done more than once. In an extreme case this could be the cause of real performance problems.
In the real world, if you are processing a lot of items and performance is a concern it's much faster to initially build a lookup:
var items = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
var lookup = items.reduce((o,i)=>o[i.id]=o,{});
you can then get at items in fixed time like this :
var bar = o[id];
You might also consider using a Map instead of an object as the lookup: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Map

Recently, I have to face the same thing in which I need to search the string from a huge array.
After some search I found It'll be easy to handle with simple code:
Code:
var items = mydata.filter(function(item){
return item.word.toLowerCase().startsWith( 'gk );
})
See https://jsfiddle.net/maheshwaghmare/cfx3p40v/4/

Iterate over any item in the array. For every item you visit, check that item's id. If it's a match, return it.
If you just want teh codez:
function getId(array, id) {
for (var i = 0, len = array.length; i < len; i++) {
if (array[i].id === id) {
return array[i];
}
}
return null; // Nothing found
}
And the same thing using ECMAScript 5's Array methods:
function getId(array, id) {
var obj = array.filter(function (val) {
return val.id === id;
});
// Filter returns an array, and we just want the matching item.
return obj[0];
}

You may try out Sugarjs from http://sugarjs.com/.
It has a very sweet method on Arrays, .find. So you can find an element like this:
array.find( {id: 75} );
You may also pass an object with more properties to it to add another "where-clause".
Note that Sugarjs extends native objects, and some people consider this very evil...

As long as the browser supports ECMA-262, 5th edition (December 2009), this should work, almost one-liner:
var bFound = myArray.some(function (obj) {
return obj.id === 45;
});

Here's how I'd go about it in pure JavaScript, in the most minimal manner I can think of that works in ECMAScript 3 or later. It returns as soon as a match is found.
var getKeyValueById = function(array, key, id) {
var testArray = array.slice(), test;
while(test = testArray.pop()) {
if (test.id === id) {
return test[key];
}
}
// return undefined if no matching id is found in array
return;
}
var myArray = [{'id':'73', 'foo':'bar'}, {'id':'45', 'foo':'bar'}]
var result = getKeyValueById(myArray, 'foo', '45');
// result is 'bar', obtained from object with id of '45'

More generic and short
function findFromArray(array,key,value) {
return array.filter(function (element) {
return element[key] == value;
}).shift();
}
in your case Ex. var element = findFromArray(myArray,'id',45) that will give you the whole element.

We can use Jquery methods $.each()/$.grep()
var data= [];
$.each(array,function(i){if(n !== 5 && i > 4){data.push(item)}}
or
var data = $.grep(array, function( n, i ) {
return ( n !== 5 && i > 4 );
});
use ES6 syntax:
Array.find, Array.filter, Array.forEach, Array.map
Or use Lodash https://lodash.com/docs/4.17.10#filter, Underscore https://underscorejs.org/#filter

Building on the accepted answer:
jQuery:
var foo = $.grep(myArray, function(e){ return e.id === foo_id})
myArray.pop(foo)
Or CoffeeScript:
foo = $.grep myArray, (e) -> e.id == foo_id
myArray.pop foo

Use Array.prototype.filter() function.
DEMO: https://jsfiddle.net/sumitridhal/r0cz0w5o/4/
JSON
var jsonObj =[
{
"name": "Me",
"info": {
"age": "15",
"favColor": "Green",
"pets": true
}
},
{
"name": "Alex",
"info": {
"age": "16",
"favColor": "orange",
"pets": false
}
},
{
"name": "Kyle",
"info": {
"age": "15",
"favColor": "Blue",
"pets": false
}
}
];
FILTER
var getPerson = function(name){
return jsonObj.filter(function(obj) {
return obj.name === name;
});
}

You can do this even in pure JavaScript by using the in built "filter" function for arrays:
Array.prototype.filterObjects = function(key, value) {
return this.filter(function(x) { return x[key] === value; })
}
So now simply pass "id" in place of key and "45" in place of value, and you will get the full object matching an id of 45. So that would be,
myArr.filterObjects("id", "45");

I really liked the answer provided by Aaron Digulla but needed to keep my array of objects so I could iterate through it later. So I modified it to
var indexer = {};
for (var i = 0; i < array.length; i++) {
indexer[array[i].id] = parseInt(i);
}
//Then you can access object properties in your array using
array[indexer[id]].property

Use:
var retObj ={};
$.each(ArrayOfObjects, function (index, obj) {
if (obj.id === '5') { // id.toString() if it is int
retObj = obj;
return false;
}
});
return retObj;
It should return an object by id.

This solution may helpful as well:
Array.prototype.grep = function (key, value) {
var that = this, ret = [];
this.forEach(function (elem, index) {
if (elem[key] === value) {
ret.push(that[index]);
}
});
return ret.length < 2 ? ret[0] : ret;
};
var bar = myArray.grep("id","45");
I made it just like $.grep and if one object is find out, function will return the object, rather than an array.

Dynamic cached find
In this solution, when we search for some object, we save it in cache. This is middle point between "always search solutions" and "create hash-map for each object in precalculations".
let cachedFind = (()=>{
let cache = new Map();
return (arr,id,el=null) =>
cache.get(id) || (el=arr.find(o=> o.id==id), cache.set(id,el), el);
})();
// ---------
// TEST
// ---------
let myArray = [...Array(100000)].map((x,i)=> ({'id':`${i}`, 'foo':`bar_${i}`}));
// example usage
console.log( cachedFind(myArray,'1234').foo );
// Benchmark
let bench = (id) => {
console.time ('time for '+id );
console.log ( cachedFind(myArray,id).foo ); // FIND
console.timeEnd('time for '+id );
}
console.log('----- no cached -----');
bench(50000);
bench(79980);
bench(99990);
console.log('----- cached -----');
bench(79980); // cached
bench(99990); // cached

callback function returning entire object instead of value [duplicate]

I've got an array:
myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}, etc.]
I'm unable to change the structure of the array. I'm being passed an id of 45, and I want to get 'bar' for that object in the array.
How do I do this in JavaScript or using jQuery?

Use the find() method:
myArray.find(x => x.id === '45').foo;
From MDN:
The find() method returns the first value in the array, if an element in the array satisfies the provided testing function. Otherwise undefined is returned.
If you want to find its index instead, use findIndex():
myArray.findIndex(x => x.id === '45');
From MDN:
The findIndex() method returns the index of the first element in the array that satisfies the provided testing function. Otherwise -1 is returned.
If you want to get an array of matching elements, use the filter() method instead:
myArray.filter(x => x.id === '45');
This will return an array of objects. If you want to get an array of foo properties, you can do this with the map() method:
myArray.filter(x => x.id === '45').map(x => x.foo);
Side note: methods like find() or filter(), and arrow functions are not supported by older browsers (like IE), so if you want to support these browsers, you should transpile your code using Babel (with the polyfill).

As you are already using jQuery, you can use the grep function which is intended for searching an array:
var result = $.grep(myArray, function(e){ return e.id == id; });
The result is an array with the items found. If you know that the object is always there and that it only occurs once, you can just use result[0].foo to get the value. Otherwise you should check the length of the resulting array. Example:
if (result.length === 0) {
// no result found
} else if (result.length === 1) {
// property found, access the foo property using result[0].foo
} else {
// multiple items found
}

Another solution is to create a lookup object:
var lookup = {};
for (var i = 0, len = array.length; i < len; i++) {
lookup[array[i].id] = array[i];
}
... now you can use lookup[id]...
This is especially interesting if you need to do many lookups.
This won't need much more memory since the IDs and objects will be shared.

ECMAScript 2015 (JavaScript ES6) provides the find()
method on arrays:
var myArray = [
{id:1, name:"bob"},
{id:2, name:"dan"},
{id:3, name:"barb"},
]
// grab the Array item which matchs the id "2"
var item = myArray.find(item => item.id === 2);
// print
console.log(item.name);
It works without external libraries. But if you want older browser support you might want to include this polyfill.

Underscore.js has a nice method for that:
myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'},etc.]
obj = _.find(myArray, function(obj) { return obj.id == '45' })

I think the easiest way would be the following, but it won't work on Internet Explorer 8 (or earlier):
var result = myArray.filter(function(v) {
return v.id === '45'; // Filter out the appropriate one
})[0].foo; // Get result and access the foo property

Try the following
function findById(source, id) {
for (var i = 0; i < source.length; i++) {
if (source[i].id === id) {
return source[i];
}
}
throw "Couldn't find object with id: " + id;
}

myArray.filter(function(a){ return a.id == some_id_you_want })[0]

A generic and more flexible version of the findById function above:
// array = [{key:value},{key:value}]
function objectFindByKey(array, key, value) {
for (var i = 0; i < array.length; i++) {
if (array[i][key] === value) {
return array[i];
}
}
return null;
}
var array = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
var result_obj = objectFindByKey(array, 'id', '45');

Performance
Today 2020.06.20 I perform test on MacOs High Sierra on Chrome 81.0, Firefox 77.0 and Safari 13.1 for chosen solutions.
Conclusions for solutions which use precalculations
Solutions with precalculations (K,L) are (much much) faster than other solutions and will not be compared with them - probably they are use some special build-in browser optimisations
surprisingly on Chrome and Safari solution based on Map (K) are much faster than solution based on object {} (L)
surprisingly on Safari for small arrays solution based on object {} (L) is slower than traditional for (E)
surprisingly on Firefox for small arrays solution based on Map (K) is slower than traditional for (E)
Conclusions when searched objects ALWAYS exists
solution which use traditional for (E) is fastest for small arrays and fast for big arrays
solution using cache (J) is fastest for big arrays - surprisingly for small arrays is medium fast
solutions based on find (A) and findIndex (B) are fast for small arras and medium fast on big arrays
solution based on $.map (H) is slowest on small arrays
solution based on reduce (D) is slowest on big arrays
Conclusions when searched objects NEVER exists
solution based on traditional for (E) is fastest on small and big arrays (except Chrome-small arrays where it is second fast)
solution based on reduce (D) is slowest on big arrays
solution which use cache (J) is medium fast but can be speed up if we save in cache also keys which have null values (which was not done here because we want to avoid unlimited memory consumption in cache in case when many not existing keys will be searched)
Details
For solutions
without precalculations: A
B
C
D
E
F
G
H
I
J (the J solution use 'inner' cache and it speed depend on how often searched elements will repeat)
with precalculations
K
L
I perform four tests. In tests I want to find 5 objects in 10 loop iterations (the objects ID not change during iterations) - so I call tested method 50 times but only first 5 times have unique id values:
small array (10 elements) and searched object ALWAYS exists - you can perform it HERE
big array (10k elements) and searched object ALWAYS exist - you can perform it HERE
small array (10 elements) and searched object NEVER exists - you can perform it HERE
big array (10k elements) and searched object NEVER exists - you can perform it HERE
Tested codes are presented below
function A(arr, id) {
return arr.find(o=> o.id==id);
}
function B(arr, id) {
let idx= arr.findIndex(o=> o.id==id);
return arr[idx];
}
function C(arr, id) {
return arr.filter(o=> o.id==id)[0];
}
function D(arr, id) {
return arr.reduce((a, b) => (a.id==id && a) || (b.id == id && b));
}
function E(arr, id) {
for (var i = 0; i < arr.length; i++) if (arr[i].id==id) return arr[i];
return null;
}
function F(arr, id) {
var retObj ={};
$.each(arr, (index, obj) => {
if (obj.id == id) {
retObj = obj;
return false;
}
});
return retObj;
}
function G(arr, id) {
return $.grep(arr, e=> e.id == id )[0];
}
function H(arr, id) {
return $.map(myArray, function(val) {
return val.id == id ? val : null;
})[0];
}
function I(arr, id) {
return _.find(arr, o => o.id==id);
}
let J = (()=>{
let cache = new Map();
return function J(arr,id,el=null) {
return cache.get(id) || (el=arr.find(o=> o.id==id), cache.set(id,el), el);
}
})();
function K(arr, id) {
return mapK.get(id)
}
function L(arr, id) {
return mapL[id];
}
// -------------
// TEST
// -------------
console.log('Find id=5');
myArray = [...Array(10)].map((x,i)=> ({'id':`${i}`, 'foo':`bar_${i}`}));
const mapK = new Map( myArray.map(el => [el.id, el]) );
const mapL = {}; myArray.forEach(el => mapL[el.id]=el);
[A,B,C,D,E,F,G,H,I,J,K,L].forEach(f=> console.log(`${f.name}: ${JSON.stringify(f(myArray, '5'))}`));
console.log('Whole array',JSON.stringify(myArray));
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.min.js"></script>
This snippet only presents tested codes
Example tests results for Chrome for small array where searched objects always exists

As others have pointed out, .find() is the way to go when looking for one object within your array. However, if your object cannot be found using this method, your program will crash:
const myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
const res = myArray.find(x => x.id === '100').foo; // Uh oh!
/*
Error:
"Uncaught TypeError: Cannot read property 'foo' of undefined"
or in newer chrome versions:
Uncaught TypeError: Cannot read properties of undefined (reading 'foo')
*/
This can be fixed by checking whether the result of .find() is defined before using .foo on it. Modern JS allows us to do this easily with optional chaining, returning undefined if the object cannot be found, rather than crashing your code:
const myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
const res = myArray.find(x => x.id === '100')?.foo; // No error!
console.log(res); // undefined when the object cannot be found

If you do this multiple times, you may set up a Map (ES6):
const map = new Map( myArray.map(el => [el.id, el]) );
Then you can simply do a O(1) lookup:
map.get(27).foo

You can get this easily using the map() function:
myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
var found = $.map(myArray, function(val) {
return val.id == 45 ? val.foo : null;
});
//found[0] == "bar";
Working example: http://jsfiddle.net/hunter/Pxaua/

Using native Array.reduce
var array = [ {'id':'73' ,'foo':'bar'} , {'id':'45' ,'foo':'bar'} , ];
var id = 73;
var found = array.reduce(function(a, b){
return (a.id==id && a) || (b.id == id && b)
});
returns the object element if found, otherwise false

You can use filters,
function getById(id, myArray) {
return myArray.filter(function(obj) {
if(obj.id == id) {
return obj
}
})[0]
}
get_my_obj = getById(73, myArray);

While there are many correct answers here, many of them do not address the fact that this is an unnecessarily expensive operation if done more than once. In an extreme case this could be the cause of real performance problems.
In the real world, if you are processing a lot of items and performance is a concern it's much faster to initially build a lookup:
var items = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
var lookup = items.reduce((o,i)=>o[i.id]=o,{});
you can then get at items in fixed time like this :
var bar = o[id];
You might also consider using a Map instead of an object as the lookup: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Map

Recently, I have to face the same thing in which I need to search the string from a huge array.
After some search I found It'll be easy to handle with simple code:
Code:
var items = mydata.filter(function(item){
return item.word.toLowerCase().startsWith( 'gk );
})
See https://jsfiddle.net/maheshwaghmare/cfx3p40v/4/

Iterate over any item in the array. For every item you visit, check that item's id. If it's a match, return it.
If you just want teh codez:
function getId(array, id) {
for (var i = 0, len = array.length; i < len; i++) {
if (array[i].id === id) {
return array[i];
}
}
return null; // Nothing found
}
And the same thing using ECMAScript 5's Array methods:
function getId(array, id) {
var obj = array.filter(function (val) {
return val.id === id;
});
// Filter returns an array, and we just want the matching item.
return obj[0];
}

You may try out Sugarjs from http://sugarjs.com/.
It has a very sweet method on Arrays, .find. So you can find an element like this:
array.find( {id: 75} );
You may also pass an object with more properties to it to add another "where-clause".
Note that Sugarjs extends native objects, and some people consider this very evil...

As long as the browser supports ECMA-262, 5th edition (December 2009), this should work, almost one-liner:
var bFound = myArray.some(function (obj) {
return obj.id === 45;
});

Here's how I'd go about it in pure JavaScript, in the most minimal manner I can think of that works in ECMAScript 3 or later. It returns as soon as a match is found.
var getKeyValueById = function(array, key, id) {
var testArray = array.slice(), test;
while(test = testArray.pop()) {
if (test.id === id) {
return test[key];
}
}
// return undefined if no matching id is found in array
return;
}
var myArray = [{'id':'73', 'foo':'bar'}, {'id':'45', 'foo':'bar'}]
var result = getKeyValueById(myArray, 'foo', '45');
// result is 'bar', obtained from object with id of '45'

More generic and short
function findFromArray(array,key,value) {
return array.filter(function (element) {
return element[key] == value;
}).shift();
}
in your case Ex. var element = findFromArray(myArray,'id',45) that will give you the whole element.

We can use Jquery methods $.each()/$.grep()
var data= [];
$.each(array,function(i){if(n !== 5 && i > 4){data.push(item)}}
or
var data = $.grep(array, function( n, i ) {
return ( n !== 5 && i > 4 );
});
use ES6 syntax:
Array.find, Array.filter, Array.forEach, Array.map
Or use Lodash https://lodash.com/docs/4.17.10#filter, Underscore https://underscorejs.org/#filter

Building on the accepted answer:
jQuery:
var foo = $.grep(myArray, function(e){ return e.id === foo_id})
myArray.pop(foo)
Or CoffeeScript:
foo = $.grep myArray, (e) -> e.id == foo_id
myArray.pop foo

Use Array.prototype.filter() function.
DEMO: https://jsfiddle.net/sumitridhal/r0cz0w5o/4/
JSON
var jsonObj =[
{
"name": "Me",
"info": {
"age": "15",
"favColor": "Green",
"pets": true
}
},
{
"name": "Alex",
"info": {
"age": "16",
"favColor": "orange",
"pets": false
}
},
{
"name": "Kyle",
"info": {
"age": "15",
"favColor": "Blue",
"pets": false
}
}
];
FILTER
var getPerson = function(name){
return jsonObj.filter(function(obj) {
return obj.name === name;
});
}

You can do this even in pure JavaScript by using the in built "filter" function for arrays:
Array.prototype.filterObjects = function(key, value) {
return this.filter(function(x) { return x[key] === value; })
}
So now simply pass "id" in place of key and "45" in place of value, and you will get the full object matching an id of 45. So that would be,
myArr.filterObjects("id", "45");

I really liked the answer provided by Aaron Digulla but needed to keep my array of objects so I could iterate through it later. So I modified it to
var indexer = {};
for (var i = 0; i < array.length; i++) {
indexer[array[i].id] = parseInt(i);
}
//Then you can access object properties in your array using
array[indexer[id]].property

Use:
var retObj ={};
$.each(ArrayOfObjects, function (index, obj) {
if (obj.id === '5') { // id.toString() if it is int
retObj = obj;
return false;
}
});
return retObj;
It should return an object by id.

This solution may helpful as well:
Array.prototype.grep = function (key, value) {
var that = this, ret = [];
this.forEach(function (elem, index) {
if (elem[key] === value) {
ret.push(that[index]);
}
});
return ret.length < 2 ? ret[0] : ret;
};
var bar = myArray.grep("id","45");
I made it just like $.grep and if one object is find out, function will return the object, rather than an array.

Dynamic cached find
In this solution, when we search for some object, we save it in cache. This is middle point between "always search solutions" and "create hash-map for each object in precalculations".
let cachedFind = (()=>{
let cache = new Map();
return (arr,id,el=null) =>
cache.get(id) || (el=arr.find(o=> o.id==id), cache.set(id,el), el);
})();
// ---------
// TEST
// ---------
let myArray = [...Array(100000)].map((x,i)=> ({'id':`${i}`, 'foo':`bar_${i}`}));
// example usage
console.log( cachedFind(myArray,'1234').foo );
// Benchmark
let bench = (id) => {
console.time ('time for '+id );
console.log ( cachedFind(myArray,id).foo ); // FIND
console.timeEnd('time for '+id );
}
console.log('----- no cached -----');
bench(50000);
bench(79980);
bench(99990);
console.log('----- cached -----');
bench(79980); // cached
bench(99990); // cached

How can I check an array for an entire object (or at least 2 key-value pairs) [in reactjs]? [duplicate]

I've got an array:
myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}, etc.]
I'm unable to change the structure of the array. I'm being passed an id of 45, and I want to get 'bar' for that object in the array.
How do I do this in JavaScript or using jQuery?

Use the find() method:
myArray.find(x => x.id === '45').foo;
From MDN:
The find() method returns the first value in the array, if an element in the array satisfies the provided testing function. Otherwise undefined is returned.
If you want to find its index instead, use findIndex():
myArray.findIndex(x => x.id === '45');
From MDN:
The findIndex() method returns the index of the first element in the array that satisfies the provided testing function. Otherwise -1 is returned.
If you want to get an array of matching elements, use the filter() method instead:
myArray.filter(x => x.id === '45');
This will return an array of objects. If you want to get an array of foo properties, you can do this with the map() method:
myArray.filter(x => x.id === '45').map(x => x.foo);
Side note: methods like find() or filter(), and arrow functions are not supported by older browsers (like IE), so if you want to support these browsers, you should transpile your code using Babel (with the polyfill).

As you are already using jQuery, you can use the grep function which is intended for searching an array:
var result = $.grep(myArray, function(e){ return e.id == id; });
The result is an array with the items found. If you know that the object is always there and that it only occurs once, you can just use result[0].foo to get the value. Otherwise you should check the length of the resulting array. Example:
if (result.length === 0) {
// no result found
} else if (result.length === 1) {
// property found, access the foo property using result[0].foo
} else {
// multiple items found
}

Another solution is to create a lookup object:
var lookup = {};
for (var i = 0, len = array.length; i < len; i++) {
lookup[array[i].id] = array[i];
}
... now you can use lookup[id]...
This is especially interesting if you need to do many lookups.
This won't need much more memory since the IDs and objects will be shared.

ECMAScript 2015 (JavaScript ES6) provides the find()
method on arrays:
var myArray = [
{id:1, name:"bob"},
{id:2, name:"dan"},
{id:3, name:"barb"},
]
// grab the Array item which matchs the id "2"
var item = myArray.find(item => item.id === 2);
// print
console.log(item.name);
It works without external libraries. But if you want older browser support you might want to include this polyfill.

Underscore.js has a nice method for that:
myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'},etc.]
obj = _.find(myArray, function(obj) { return obj.id == '45' })

I think the easiest way would be the following, but it won't work on Internet Explorer 8 (or earlier):
var result = myArray.filter(function(v) {
return v.id === '45'; // Filter out the appropriate one
})[0].foo; // Get result and access the foo property

Try the following
function findById(source, id) {
for (var i = 0; i < source.length; i++) {
if (source[i].id === id) {
return source[i];
}
}
throw "Couldn't find object with id: " + id;
}

myArray.filter(function(a){ return a.id == some_id_you_want })[0]

A generic and more flexible version of the findById function above:
// array = [{key:value},{key:value}]
function objectFindByKey(array, key, value) {
for (var i = 0; i < array.length; i++) {
if (array[i][key] === value) {
return array[i];
}
}
return null;
}
var array = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
var result_obj = objectFindByKey(array, 'id', '45');

Performance
Today 2020.06.20 I perform test on MacOs High Sierra on Chrome 81.0, Firefox 77.0 and Safari 13.1 for chosen solutions.
Conclusions for solutions which use precalculations
Solutions with precalculations (K,L) are (much much) faster than other solutions and will not be compared with them - probably they are use some special build-in browser optimisations
surprisingly on Chrome and Safari solution based on Map (K) are much faster than solution based on object {} (L)
surprisingly on Safari for small arrays solution based on object {} (L) is slower than traditional for (E)
surprisingly on Firefox for small arrays solution based on Map (K) is slower than traditional for (E)
Conclusions when searched objects ALWAYS exists
solution which use traditional for (E) is fastest for small arrays and fast for big arrays
solution using cache (J) is fastest for big arrays - surprisingly for small arrays is medium fast
solutions based on find (A) and findIndex (B) are fast for small arras and medium fast on big arrays
solution based on $.map (H) is slowest on small arrays
solution based on reduce (D) is slowest on big arrays
Conclusions when searched objects NEVER exists
solution based on traditional for (E) is fastest on small and big arrays (except Chrome-small arrays where it is second fast)
solution based on reduce (D) is slowest on big arrays
solution which use cache (J) is medium fast but can be speed up if we save in cache also keys which have null values (which was not done here because we want to avoid unlimited memory consumption in cache in case when many not existing keys will be searched)
Details
For solutions
without precalculations: A
B
C
D
E
F
G
H
I
J (the J solution use 'inner' cache and it speed depend on how often searched elements will repeat)
with precalculations
K
L
I perform four tests. In tests I want to find 5 objects in 10 loop iterations (the objects ID not change during iterations) - so I call tested method 50 times but only first 5 times have unique id values:
small array (10 elements) and searched object ALWAYS exists - you can perform it HERE
big array (10k elements) and searched object ALWAYS exist - you can perform it HERE
small array (10 elements) and searched object NEVER exists - you can perform it HERE
big array (10k elements) and searched object NEVER exists - you can perform it HERE
Tested codes are presented below
function A(arr, id) {
return arr.find(o=> o.id==id);
}
function B(arr, id) {
let idx= arr.findIndex(o=> o.id==id);
return arr[idx];
}
function C(arr, id) {
return arr.filter(o=> o.id==id)[0];
}
function D(arr, id) {
return arr.reduce((a, b) => (a.id==id && a) || (b.id == id && b));
}
function E(arr, id) {
for (var i = 0; i < arr.length; i++) if (arr[i].id==id) return arr[i];
return null;
}
function F(arr, id) {
var retObj ={};
$.each(arr, (index, obj) => {
if (obj.id == id) {
retObj = obj;
return false;
}
});
return retObj;
}
function G(arr, id) {
return $.grep(arr, e=> e.id == id )[0];
}
function H(arr, id) {
return $.map(myArray, function(val) {
return val.id == id ? val : null;
})[0];
}
function I(arr, id) {
return _.find(arr, o => o.id==id);
}
let J = (()=>{
let cache = new Map();
return function J(arr,id,el=null) {
return cache.get(id) || (el=arr.find(o=> o.id==id), cache.set(id,el), el);
}
})();
function K(arr, id) {
return mapK.get(id)
}
function L(arr, id) {
return mapL[id];
}
// -------------
// TEST
// -------------
console.log('Find id=5');
myArray = [...Array(10)].map((x,i)=> ({'id':`${i}`, 'foo':`bar_${i}`}));
const mapK = new Map( myArray.map(el => [el.id, el]) );
const mapL = {}; myArray.forEach(el => mapL[el.id]=el);
[A,B,C,D,E,F,G,H,I,J,K,L].forEach(f=> console.log(`${f.name}: ${JSON.stringify(f(myArray, '5'))}`));
console.log('Whole array',JSON.stringify(myArray));
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.min.js"></script>
This snippet only presents tested codes
Example tests results for Chrome for small array where searched objects always exists

As others have pointed out, .find() is the way to go when looking for one object within your array. However, if your object cannot be found using this method, your program will crash:
const myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
const res = myArray.find(x => x.id === '100').foo; // Uh oh!
/*
Error:
"Uncaught TypeError: Cannot read property 'foo' of undefined"
or in newer chrome versions:
Uncaught TypeError: Cannot read properties of undefined (reading 'foo')
*/
This can be fixed by checking whether the result of .find() is defined before using .foo on it. Modern JS allows us to do this easily with optional chaining, returning undefined if the object cannot be found, rather than crashing your code:
const myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
const res = myArray.find(x => x.id === '100')?.foo; // No error!
console.log(res); // undefined when the object cannot be found

If you do this multiple times, you may set up a Map (ES6):
const map = new Map( myArray.map(el => [el.id, el]) );
Then you can simply do a O(1) lookup:
map.get(27).foo

You can get this easily using the map() function:
myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
var found = $.map(myArray, function(val) {
return val.id == 45 ? val.foo : null;
});
//found[0] == "bar";
Working example: http://jsfiddle.net/hunter/Pxaua/

Using native Array.reduce
var array = [ {'id':'73' ,'foo':'bar'} , {'id':'45' ,'foo':'bar'} , ];
var id = 73;
var found = array.reduce(function(a, b){
return (a.id==id && a) || (b.id == id && b)
});
returns the object element if found, otherwise false

You can use filters,
function getById(id, myArray) {
return myArray.filter(function(obj) {
if(obj.id == id) {
return obj
}
})[0]
}
get_my_obj = getById(73, myArray);

While there are many correct answers here, many of them do not address the fact that this is an unnecessarily expensive operation if done more than once. In an extreme case this could be the cause of real performance problems.
In the real world, if you are processing a lot of items and performance is a concern it's much faster to initially build a lookup:
var items = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
var lookup = items.reduce((o,i)=>o[i.id]=o,{});
you can then get at items in fixed time like this :
var bar = o[id];
You might also consider using a Map instead of an object as the lookup: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Map

Recently, I have to face the same thing in which I need to search the string from a huge array.
After some search I found It'll be easy to handle with simple code:
Code:
var items = mydata.filter(function(item){
return item.word.toLowerCase().startsWith( 'gk );
})
See https://jsfiddle.net/maheshwaghmare/cfx3p40v/4/

Iterate over any item in the array. For every item you visit, check that item's id. If it's a match, return it.
If you just want teh codez:
function getId(array, id) {
for (var i = 0, len = array.length; i < len; i++) {
if (array[i].id === id) {
return array[i];
}
}
return null; // Nothing found
}
And the same thing using ECMAScript 5's Array methods:
function getId(array, id) {
var obj = array.filter(function (val) {
return val.id === id;
});
// Filter returns an array, and we just want the matching item.
return obj[0];
}

You may try out Sugarjs from http://sugarjs.com/.
It has a very sweet method on Arrays, .find. So you can find an element like this:
array.find( {id: 75} );
You may also pass an object with more properties to it to add another "where-clause".
Note that Sugarjs extends native objects, and some people consider this very evil...

As long as the browser supports ECMA-262, 5th edition (December 2009), this should work, almost one-liner:
var bFound = myArray.some(function (obj) {
return obj.id === 45;
});

Here's how I'd go about it in pure JavaScript, in the most minimal manner I can think of that works in ECMAScript 3 or later. It returns as soon as a match is found.
var getKeyValueById = function(array, key, id) {
var testArray = array.slice(), test;
while(test = testArray.pop()) {
if (test.id === id) {
return test[key];
}
}
// return undefined if no matching id is found in array
return;
}
var myArray = [{'id':'73', 'foo':'bar'}, {'id':'45', 'foo':'bar'}]
var result = getKeyValueById(myArray, 'foo', '45');
// result is 'bar', obtained from object with id of '45'

More generic and short
function findFromArray(array,key,value) {
return array.filter(function (element) {
return element[key] == value;
}).shift();
}
in your case Ex. var element = findFromArray(myArray,'id',45) that will give you the whole element.

We can use Jquery methods $.each()/$.grep()
var data= [];
$.each(array,function(i){if(n !== 5 && i > 4){data.push(item)}}
or
var data = $.grep(array, function( n, i ) {
return ( n !== 5 && i > 4 );
});
use ES6 syntax:
Array.find, Array.filter, Array.forEach, Array.map
Or use Lodash https://lodash.com/docs/4.17.10#filter, Underscore https://underscorejs.org/#filter

Building on the accepted answer:
jQuery:
var foo = $.grep(myArray, function(e){ return e.id === foo_id})
myArray.pop(foo)
Or CoffeeScript:
foo = $.grep myArray, (e) -> e.id == foo_id
myArray.pop foo

Use Array.prototype.filter() function.
DEMO: https://jsfiddle.net/sumitridhal/r0cz0w5o/4/
JSON
var jsonObj =[
{
"name": "Me",
"info": {
"age": "15",
"favColor": "Green",
"pets": true
}
},
{
"name": "Alex",
"info": {
"age": "16",
"favColor": "orange",
"pets": false
}
},
{
"name": "Kyle",
"info": {
"age": "15",
"favColor": "Blue",
"pets": false
}
}
];
FILTER
var getPerson = function(name){
return jsonObj.filter(function(obj) {
return obj.name === name;
});
}

You can do this even in pure JavaScript by using the in built "filter" function for arrays:
Array.prototype.filterObjects = function(key, value) {
return this.filter(function(x) { return x[key] === value; })
}
So now simply pass "id" in place of key and "45" in place of value, and you will get the full object matching an id of 45. So that would be,
myArr.filterObjects("id", "45");

I really liked the answer provided by Aaron Digulla but needed to keep my array of objects so I could iterate through it later. So I modified it to
var indexer = {};
for (var i = 0; i < array.length; i++) {
indexer[array[i].id] = parseInt(i);
}
//Then you can access object properties in your array using
array[indexer[id]].property

Use:
var retObj ={};
$.each(ArrayOfObjects, function (index, obj) {
if (obj.id === '5') { // id.toString() if it is int
retObj = obj;
return false;
}
});
return retObj;
It should return an object by id.

This solution may helpful as well:
Array.prototype.grep = function (key, value) {
var that = this, ret = [];
this.forEach(function (elem, index) {
if (elem[key] === value) {
ret.push(that[index]);
}
});
return ret.length < 2 ? ret[0] : ret;
};
var bar = myArray.grep("id","45");
I made it just like $.grep and if one object is find out, function will return the object, rather than an array.

Dynamic cached find
In this solution, when we search for some object, we save it in cache. This is middle point between "always search solutions" and "create hash-map for each object in precalculations".
let cachedFind = (()=>{
let cache = new Map();
return (arr,id,el=null) =>
cache.get(id) || (el=arr.find(o=> o.id==id), cache.set(id,el), el);
})();
// ---------
// TEST
// ---------
let myArray = [...Array(100000)].map((x,i)=> ({'id':`${i}`, 'foo':`bar_${i}`}));
// example usage
console.log( cachedFind(myArray,'1234').foo );
// Benchmark
let bench = (id) => {
console.time ('time for '+id );
console.log ( cachedFind(myArray,id).foo ); // FIND
console.timeEnd('time for '+id );
}
console.log('----- no cached -----');
bench(50000);
bench(79980);
bench(99990);
console.log('----- cached -----');
bench(79980); // cached
bench(99990); // cached

Alter object value base on object value [duplicate]

I've got an array:
myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}, etc.]
I'm unable to change the structure of the array. I'm being passed an id of 45, and I want to get 'bar' for that object in the array.
How do I do this in JavaScript or using jQuery?

Use the find() method:
myArray.find(x => x.id === '45').foo;
From MDN:
The find() method returns the first value in the array, if an element in the array satisfies the provided testing function. Otherwise undefined is returned.
If you want to find its index instead, use findIndex():
myArray.findIndex(x => x.id === '45');
From MDN:
The findIndex() method returns the index of the first element in the array that satisfies the provided testing function. Otherwise -1 is returned.
If you want to get an array of matching elements, use the filter() method instead:
myArray.filter(x => x.id === '45');
This will return an array of objects. If you want to get an array of foo properties, you can do this with the map() method:
myArray.filter(x => x.id === '45').map(x => x.foo);
Side note: methods like find() or filter(), and arrow functions are not supported by older browsers (like IE), so if you want to support these browsers, you should transpile your code using Babel (with the polyfill).

As you are already using jQuery, you can use the grep function which is intended for searching an array:
var result = $.grep(myArray, function(e){ return e.id == id; });
The result is an array with the items found. If you know that the object is always there and that it only occurs once, you can just use result[0].foo to get the value. Otherwise you should check the length of the resulting array. Example:
if (result.length === 0) {
// no result found
} else if (result.length === 1) {
// property found, access the foo property using result[0].foo
} else {
// multiple items found
}

Another solution is to create a lookup object:
var lookup = {};
for (var i = 0, len = array.length; i < len; i++) {
lookup[array[i].id] = array[i];
}
... now you can use lookup[id]...
This is especially interesting if you need to do many lookups.
This won't need much more memory since the IDs and objects will be shared.

ECMAScript 2015 (JavaScript ES6) provides the find()
method on arrays:
var myArray = [
{id:1, name:"bob"},
{id:2, name:"dan"},
{id:3, name:"barb"},
]
// grab the Array item which matchs the id "2"
var item = myArray.find(item => item.id === 2);
// print
console.log(item.name);
It works without external libraries. But if you want older browser support you might want to include this polyfill.

Underscore.js has a nice method for that:
myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'},etc.]
obj = _.find(myArray, function(obj) { return obj.id == '45' })

I think the easiest way would be the following, but it won't work on Internet Explorer 8 (or earlier):
var result = myArray.filter(function(v) {
return v.id === '45'; // Filter out the appropriate one
})[0].foo; // Get result and access the foo property

Try the following
function findById(source, id) {
for (var i = 0; i < source.length; i++) {
if (source[i].id === id) {
return source[i];
}
}
throw "Couldn't find object with id: " + id;
}

myArray.filter(function(a){ return a.id == some_id_you_want })[0]

A generic and more flexible version of the findById function above:
// array = [{key:value},{key:value}]
function objectFindByKey(array, key, value) {
for (var i = 0; i < array.length; i++) {
if (array[i][key] === value) {
return array[i];
}
}
return null;
}
var array = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
var result_obj = objectFindByKey(array, 'id', '45');

Performance
Today 2020.06.20 I perform test on MacOs High Sierra on Chrome 81.0, Firefox 77.0 and Safari 13.1 for chosen solutions.
Conclusions for solutions which use precalculations
Solutions with precalculations (K,L) are (much much) faster than other solutions and will not be compared with them - probably they are use some special build-in browser optimisations
surprisingly on Chrome and Safari solution based on Map (K) are much faster than solution based on object {} (L)
surprisingly on Safari for small arrays solution based on object {} (L) is slower than traditional for (E)
surprisingly on Firefox for small arrays solution based on Map (K) is slower than traditional for (E)
Conclusions when searched objects ALWAYS exists
solution which use traditional for (E) is fastest for small arrays and fast for big arrays
solution using cache (J) is fastest for big arrays - surprisingly for small arrays is medium fast
solutions based on find (A) and findIndex (B) are fast for small arras and medium fast on big arrays
solution based on $.map (H) is slowest on small arrays
solution based on reduce (D) is slowest on big arrays
Conclusions when searched objects NEVER exists
solution based on traditional for (E) is fastest on small and big arrays (except Chrome-small arrays where it is second fast)
solution based on reduce (D) is slowest on big arrays
solution which use cache (J) is medium fast but can be speed up if we save in cache also keys which have null values (which was not done here because we want to avoid unlimited memory consumption in cache in case when many not existing keys will be searched)
Details
For solutions
without precalculations: A
B
C
D
E
F
G
H
I
J (the J solution use 'inner' cache and it speed depend on how often searched elements will repeat)
with precalculations
K
L
I perform four tests. In tests I want to find 5 objects in 10 loop iterations (the objects ID not change during iterations) - so I call tested method 50 times but only first 5 times have unique id values:
small array (10 elements) and searched object ALWAYS exists - you can perform it HERE
big array (10k elements) and searched object ALWAYS exist - you can perform it HERE
small array (10 elements) and searched object NEVER exists - you can perform it HERE
big array (10k elements) and searched object NEVER exists - you can perform it HERE
Tested codes are presented below
function A(arr, id) {
return arr.find(o=> o.id==id);
}
function B(arr, id) {
let idx= arr.findIndex(o=> o.id==id);
return arr[idx];
}
function C(arr, id) {
return arr.filter(o=> o.id==id)[0];
}
function D(arr, id) {
return arr.reduce((a, b) => (a.id==id && a) || (b.id == id && b));
}
function E(arr, id) {
for (var i = 0; i < arr.length; i++) if (arr[i].id==id) return arr[i];
return null;
}
function F(arr, id) {
var retObj ={};
$.each(arr, (index, obj) => {
if (obj.id == id) {
retObj = obj;
return false;
}
});
return retObj;
}
function G(arr, id) {
return $.grep(arr, e=> e.id == id )[0];
}
function H(arr, id) {
return $.map(myArray, function(val) {
return val.id == id ? val : null;
})[0];
}
function I(arr, id) {
return _.find(arr, o => o.id==id);
}
let J = (()=>{
let cache = new Map();
return function J(arr,id,el=null) {
return cache.get(id) || (el=arr.find(o=> o.id==id), cache.set(id,el), el);
}
})();
function K(arr, id) {
return mapK.get(id)
}
function L(arr, id) {
return mapL[id];
}
// -------------
// TEST
// -------------
console.log('Find id=5');
myArray = [...Array(10)].map((x,i)=> ({'id':`${i}`, 'foo':`bar_${i}`}));
const mapK = new Map( myArray.map(el => [el.id, el]) );
const mapL = {}; myArray.forEach(el => mapL[el.id]=el);
[A,B,C,D,E,F,G,H,I,J,K,L].forEach(f=> console.log(`${f.name}: ${JSON.stringify(f(myArray, '5'))}`));
console.log('Whole array',JSON.stringify(myArray));
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.min.js"></script>
This snippet only presents tested codes
Example tests results for Chrome for small array where searched objects always exists

As others have pointed out, .find() is the way to go when looking for one object within your array. However, if your object cannot be found using this method, your program will crash:
const myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
const res = myArray.find(x => x.id === '100').foo; // Uh oh!
/*
Error:
"Uncaught TypeError: Cannot read property 'foo' of undefined"
or in newer chrome versions:
Uncaught TypeError: Cannot read properties of undefined (reading 'foo')
*/
This can be fixed by checking whether the result of .find() is defined before using .foo on it. Modern JS allows us to do this easily with optional chaining, returning undefined if the object cannot be found, rather than crashing your code:
const myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
const res = myArray.find(x => x.id === '100')?.foo; // No error!
console.log(res); // undefined when the object cannot be found

If you do this multiple times, you may set up a Map (ES6):
const map = new Map( myArray.map(el => [el.id, el]) );
Then you can simply do a O(1) lookup:
map.get(27).foo

You can get this easily using the map() function:
myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
var found = $.map(myArray, function(val) {
return val.id == 45 ? val.foo : null;
});
//found[0] == "bar";
Working example: http://jsfiddle.net/hunter/Pxaua/

Using native Array.reduce
var array = [ {'id':'73' ,'foo':'bar'} , {'id':'45' ,'foo':'bar'} , ];
var id = 73;
var found = array.reduce(function(a, b){
return (a.id==id && a) || (b.id == id && b)
});
returns the object element if found, otherwise false

You can use filters,
function getById(id, myArray) {
return myArray.filter(function(obj) {
if(obj.id == id) {
return obj
}
})[0]
}
get_my_obj = getById(73, myArray);

While there are many correct answers here, many of them do not address the fact that this is an unnecessarily expensive operation if done more than once. In an extreme case this could be the cause of real performance problems.
In the real world, if you are processing a lot of items and performance is a concern it's much faster to initially build a lookup:
var items = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
var lookup = items.reduce((o,i)=>o[i.id]=o,{});
you can then get at items in fixed time like this :
var bar = o[id];
You might also consider using a Map instead of an object as the lookup: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Map

Recently, I have to face the same thing in which I need to search the string from a huge array.
After some search I found It'll be easy to handle with simple code:
Code:
var items = mydata.filter(function(item){
return item.word.toLowerCase().startsWith( 'gk );
})
See https://jsfiddle.net/maheshwaghmare/cfx3p40v/4/

Iterate over any item in the array. For every item you visit, check that item's id. If it's a match, return it.
If you just want teh codez:
function getId(array, id) {
for (var i = 0, len = array.length; i < len; i++) {
if (array[i].id === id) {
return array[i];
}
}
return null; // Nothing found
}
And the same thing using ECMAScript 5's Array methods:
function getId(array, id) {
var obj = array.filter(function (val) {
return val.id === id;
});
// Filter returns an array, and we just want the matching item.
return obj[0];
}

You may try out Sugarjs from http://sugarjs.com/.
It has a very sweet method on Arrays, .find. So you can find an element like this:
array.find( {id: 75} );
You may also pass an object with more properties to it to add another "where-clause".
Note that Sugarjs extends native objects, and some people consider this very evil...

As long as the browser supports ECMA-262, 5th edition (December 2009), this should work, almost one-liner:
var bFound = myArray.some(function (obj) {
return obj.id === 45;
});

Here's how I'd go about it in pure JavaScript, in the most minimal manner I can think of that works in ECMAScript 3 or later. It returns as soon as a match is found.
var getKeyValueById = function(array, key, id) {
var testArray = array.slice(), test;
while(test = testArray.pop()) {
if (test.id === id) {
return test[key];
}
}
// return undefined if no matching id is found in array
return;
}
var myArray = [{'id':'73', 'foo':'bar'}, {'id':'45', 'foo':'bar'}]
var result = getKeyValueById(myArray, 'foo', '45');
// result is 'bar', obtained from object with id of '45'

More generic and short
function findFromArray(array,key,value) {
return array.filter(function (element) {
return element[key] == value;
}).shift();
}
in your case Ex. var element = findFromArray(myArray,'id',45) that will give you the whole element.

We can use Jquery methods $.each()/$.grep()
var data= [];
$.each(array,function(i){if(n !== 5 && i > 4){data.push(item)}}
or
var data = $.grep(array, function( n, i ) {
return ( n !== 5 && i > 4 );
});
use ES6 syntax:
Array.find, Array.filter, Array.forEach, Array.map
Or use Lodash https://lodash.com/docs/4.17.10#filter, Underscore https://underscorejs.org/#filter

Building on the accepted answer:
jQuery:
var foo = $.grep(myArray, function(e){ return e.id === foo_id})
myArray.pop(foo)
Or CoffeeScript:
foo = $.grep myArray, (e) -> e.id == foo_id
myArray.pop foo

Use Array.prototype.filter() function.
DEMO: https://jsfiddle.net/sumitridhal/r0cz0w5o/4/
JSON
var jsonObj =[
{
"name": "Me",
"info": {
"age": "15",
"favColor": "Green",
"pets": true
}
},
{
"name": "Alex",
"info": {
"age": "16",
"favColor": "orange",
"pets": false
}
},
{
"name": "Kyle",
"info": {
"age": "15",
"favColor": "Blue",
"pets": false
}
}
];
FILTER
var getPerson = function(name){
return jsonObj.filter(function(obj) {
return obj.name === name;
});
}

You can do this even in pure JavaScript by using the in built "filter" function for arrays:
Array.prototype.filterObjects = function(key, value) {
return this.filter(function(x) { return x[key] === value; })
}
So now simply pass "id" in place of key and "45" in place of value, and you will get the full object matching an id of 45. So that would be,
myArr.filterObjects("id", "45");

I really liked the answer provided by Aaron Digulla but needed to keep my array of objects so I could iterate through it later. So I modified it to
var indexer = {};
for (var i = 0; i < array.length; i++) {
indexer[array[i].id] = parseInt(i);
}
//Then you can access object properties in your array using
array[indexer[id]].property

Use:
var retObj ={};
$.each(ArrayOfObjects, function (index, obj) {
if (obj.id === '5') { // id.toString() if it is int
retObj = obj;
return false;
}
});
return retObj;
It should return an object by id.

This solution may helpful as well:
Array.prototype.grep = function (key, value) {
var that = this, ret = [];
this.forEach(function (elem, index) {
if (elem[key] === value) {
ret.push(that[index]);
}
});
return ret.length < 2 ? ret[0] : ret;
};
var bar = myArray.grep("id","45");
I made it just like $.grep and if one object is find out, function will return the object, rather than an array.

Dynamic cached find
In this solution, when we search for some object, we save it in cache. This is middle point between "always search solutions" and "create hash-map for each object in precalculations".
let cachedFind = (()=>{
let cache = new Map();
return (arr,id,el=null) =>
cache.get(id) || (el=arr.find(o=> o.id==id), cache.set(id,el), el);
})();
// ---------
// TEST
// ---------
let myArray = [...Array(100000)].map((x,i)=> ({'id':`${i}`, 'foo':`bar_${i}`}));
// example usage
console.log( cachedFind(myArray,'1234').foo );
// Benchmark
let bench = (id) => {
console.time ('time for '+id );
console.log ( cachedFind(myArray,id).foo ); // FIND
console.timeEnd('time for '+id );
}
console.log('----- no cached -----');
bench(50000);
bench(79980);
bench(99990);
console.log('----- cached -----');
bench(79980); // cached
bench(99990); // cached

How to create a list of unique items in JavaScript? [duplicate]

This question already has answers here:
Get all unique values in a JavaScript array (remove duplicates)
(91 answers)
Closed 1 year ago.
In my CouchDB reduce function I need to reduce a list of items to the unique ones.
Note: In that case it's ok to have a list, it will be a small number of items of string type.
My current way is to set keys of a object, then return the keys of that object
since the place the code can't use things like _.uniq for example.
I'd like to find a more elegant way to spell it than this.
function(keys, values, rereduce) {
// values is a Array of Arrays
values = Array.concat.apply(null, values);
var uniq = {};
values.forEach(function(item) { uniq[item] = true; });
return Object.keys(uniq);
}

The best method seem to be using ES6 and Set. Single line and faster* than above according to fiddle
const myList = [1,4,5,1,2,4,5,6,7];
const unique = [...new Set(myList)];
console.log(unique);
*tested in safari

2021 answer:
const unique = (arr) => [...new Set(arr)];
unique([1, 2, 2, 3, 4, 4, 5, 1]); // [1, 2, 3, 4, 5]
Here you just create a set from the given array and then convert it back to the array.
I measured performance and it's almost twice faster now than the approach proposed in the old answer I posted before. Also, it's just a one-liner.
Updated fiddle
Old answer just for the record:
Commonly, the approach you used is a good idea.
But I could propose a solution that will make the algorithm a lot faster.
function unique(arr) {
var u = {}, a = [];
for(var i = 0, l = arr.length; i < l; ++i){
if(!u.hasOwnProperty(arr[i])) {
a.push(arr[i]);
u[arr[i]] = 1;
}
}
return a;
}
As you can see we have only one loop here.
I've made an example that is testing both your and my solutions. Try to play with it.

An alternative that's suitable for small lists would be to ape the Unix command line approach of sort | uniq:
function unique(a) {
return a.sort().filter(function(value, index, array) {
return (index === 0) || (value !== array[index-1]);
});
}
This function sorts the argument, and then filters the result to omit any items that are equal to their predecessor.
The keys-based approach is fine, and will have better performance characteristics for large numbers of items (O(n) for inserting n items into a hashtable, compared to O(n log n) for sorting the array). However, this is unlikely to be noticeable on small lists. Moreover, with this version you could modify it to use a different sorting or equality function if necessary; with hash keys you're stuck with JavaScripts notion of key equality.

This should work with anything, not just strings:
export const getUniqueList = (a: Array<any>) : Array<any> => {
const set = new Set<any>();
for(let v of a){
set.add(v);
}
return Array.from(set);
};
the above can just be reduced to:
export const getUniqueValues = (a: Array<any>) => {
return Array.from(new Set(a));
};
:)

To get unique objects, you can use JSON.stringify and JSON.parse:
const arr = [{test: "a"}, {test: "a"}];
const unique = Array.from(new Set(arr.map(JSON.stringify))).map(JSON.parse);
console.log(unique);

Using Object.keys will give you strings if you put in integer arguments (uniq([1,2,3]) => ['1','2','3']. Here's one with Array.reduce:
function uniq(list) {
return list.reduce((acc, d) => acc.includes(d) ? acc : acc.concat(d), []);
}

This is an old question, I know. However, it is at the top of some google searches, so I wanted to add that you can combine the answers from #RobHague and #EugeneNaydenov using the following:
function unique(arr) {
const u = {};
return arr.filter((v) => {
return u[v] = !u.hasOwnProperty(v);
});
};
You can also ignore undefined values (often handy) by adding:
function unique(arr) {
const u = {};
return arr.filter((v) => {
return u[v] = (v !== undefined && !u.hasOwnProperty(v));
});
};
You can play with this solution here: https://jsfiddle.net/s8d14v5n/

I find the other answers to be rather complicated for no gain that I can see.
We can use the indexOf method of the Array to verify if an item exists in it before pushing:
const duplicated_values = ['one', 'one', 'one', 'one', 'two', 'three', 'three', 'four'];
const unique_list = [];
duplicated_values.forEach(value => {
if (unique_list.indexOf(value) === -1) {
unique_list.push(value);
}
});
console.log(unique_list);
That will work with any type of variable as well, even objects (given the identifier actually reference the same entity, merely equivalent objects are not seen as the same).

what about
function unique(list) {
for (i = 0; i<list.length; i++) {
for (j=i+1; j<list.length; j++) {
if (list[i] == list[j]) {
list.splice(j, 1);
}
}
}
}