I have this code:
//Arguments are unique.
var Object1 = new Object(argument,argument,argument);
var Object2 = new Object(argument,argument,argument);
var Object3 = new Object(argument,argument,argument);
//...
var Object100 new Object(argument,argument,argument);
function convert(){
var array = ["Object1","Object56"];
// Manipulate values in array above as if they were the objects already
//declared above this function, like acessing "Object56.argument" property.
}
I need to convert the the strings in the array to the objects that have already been declared, in order to manipulate the objects properties (which are converted from the arguments) in a function. I realize I'm basically turning JS objects into a database which is probably a bad idea but I was wondering if there's a solution to this? They way the values in the array are chosen is fairly complex and I think it would detract from the question, but they are randomly generated more or less.
Instead of storing each object as a separate variable, create a map:
var objectMap = {
Object1: new Object(argument, argument, argument),
Object2: new Object(argument, argument, argument),
// ...
Object100: new Object(argument, argument, argument)
};
The mapping would then be easy enough.
You can either do it manually:
var array = ['Object1', 'Object2'];
var objects = [];
for(var i = 0; i < array.length; i++) {
var key = array[i];
objects.push(objectMap[key]);
}
Or (if you're supporting ES5) use the map function:
var array = ['Object1', 'Object2'];
var objects = array.map(function (key) {
return objectMap[key];
});
Related
This question already has answers here:
Copy array by value
(39 answers)
Closed 8 years ago.
I have an array example fruit . I'd like to copy it as array fruits2, without keeping reference.
As in the following example reference is kept so fruits is modified.
var fruit = function (name){
this.name = name;
}
var fruits = [];
fruits.push(new fruit('apple'));
fruits.push(new fruit('banana'));
fruits.push(new fruit('orange'));
var fruits2 = fruits;
fruits2.length = 0;
console.log(fruits);
http://jsfiddle.net/vkdqur82/
Using JSON.stringify and JSON.parse does the trick but the objects in fruits2 are not any longer of type fruit but are of general type object
var temp = JSON.stringify(fruits);
var fruits2 = JSON.parse(temp);
I would like to know an alternative approach which would keep inner object of fruit.
Use slice: var fruits2 = fruits.slice(); should do it.
Your jsFiddle, modified
See also: MDN
**Edit. I was a bit lazy, let's correct my answer to make up for that.
For an Array of just values slice is perfect. For an Array of objects or arrays or a mix of values/objects/arrays, the Array and Object elements of the Array to clone need cloning too. Otherwise they will be references to the original arrays or objects (so: not copies) and a change of one [of these references of arrays or objects] will be reflected in all 'clones' containing a reference to it.
To clone an Array of Arrays/Objects/mixed values Array.map is your friend. There are several methods to think of:
creating a new instance with old data
var fruits1 = fruits.map(function(v) {return new Fruit(v.name);});
using JSON
var fruits2 = fruits.map(function(v) {return JSON.parse(JSON.stringify(v));});
create and use some cloning method
var fruits3 = fruits.map(function(v) {return cloneObj(v);});
In case 3, a method for cloning could look like:
function cloneObj(obj) {
function clone(o, curr) {
for (var l in o){
if (o[l] instanceof Object) {
curr[l] = cloneObj(o[l]);
} else {
curr[l] = o[l];
}
}
return curr;
}
return obj instanceof Array
? obj.slice().map( function (v) { return cloneObj(v); } )
: obj instanceof Object
? clone(obj, {})
: obj;
}
Using this cloneObj method, Array.map is obsolete.
You can also use var fruitsx = cloneObj(fruits);
The jsFiddle from the link above is modified to demonstrate these methods.
For Array.map, see again MDN
slice can do the trick.
You can also use .map but .slice is normally faster.
var copy = fruits.map(function(item) {return item});
Hope it helps
You can declare a new array and use concat method, so that you concat all values from your array to the new array. Something like this:
var x = ["a","b"];
var a = [];
a = a.concat(x);
console.log(a);
I edited my poor answer.
Best regards.
I have rootObject which holds childObject as a value. I use two for loops to get values from childObject and put them to array. Array is cleared in every iteration of outer loop.
var childObject = new Object();
for (var i = 0; i < 3; ++i) {
childObject[i] = i*i;
}
var rootObject = new Object();
rootObject[0] = childObject;
I am using console.log(resultArray) to observe array. And this is what I got:
When clearing before second for loop
var resultArray = []
for ( var rootKey in rootObject){
resultArray.length = 0; //clearing array
for ( var childKey in rootObject[rootKey]){
resultArray.push([ parseInt(childKey), rootObject[rootKey][childKey] ]);
}
console.log(resultArray);
}
I get [Array[2], Array[2], Array[2]
When clearing after second for loop
var resultArray = []
for ( var rootKey in rootObject){
for ( var childKey in rootObject[rootKey]){
resultArray.push([ parseInt(childKey), rootObject[rootKey][childKey] ]);
}
console.log(resultArray);
resultArray.length = 0; //clearing array
}
I get []
Why result is different?
EDIT
I am using Firefox 29
http://jsfiddle.net/xf78k/5/ <-- good
http://jsfiddle.net/xf78k/6/ <-- bad
You store a reference to the array into your var, and print it through the console, that will show you the realtime (dynamic) state of the array.
In other words, the console will show you three times the same objects, in both cases, and its state will be the final state of resultArray.
If you converted it to string, or printed its length, you'd have the expected result, because it would be a primitive value, and the console wouldn't keep track of its reference.
Taste the difference:
var childObject = new Object();
for (var i = 0; i < 3; ++i) {
childObject[i] = i*i;
}
var rootObject = new Object();
rootObject[0] = childObject;
var resultArray = []
for ( var rootKey in rootObject){
for ( var childKey in rootObject[rootKey]){
resultArray.push([ parseInt(childKey), rootObject[rootKey][childKey] ]);
}
console.log(resultArray.length);
resultArray.length = 0; //clearing array
}
One suggestion: don't initialize plain objects with "new Object()".
var childObject = {};
is to be preferred instead.
EDIT: why you'd rather prefer the literal syntax to init objects
Try this code:
var a = new Object(1);
var b = new Object("1");
The result is that a is a Number(), and b is a String, because Object accept an optional parameter that drives which constructor is used for the object.
So, it is error prone.
Now try this:
Object = function () {
//xmlhttp=new XMLHttpRequest("malicious site"); ...
console.log("XSS attack")
}
var c = new Object();
any script can override it, while {} is safer.
Finally, due to JS engines optimization, the literal syntax leads to better performance.
More
console.log does lazy and async evaluation of variables. Since arrays are passed by reference, it's not strange for it to reflex the value it has after clearance.
If you insert a breakpoint before clearing you should see the array with its elements.
I am having an issue with the following code:
var samount = [{value:100, name:'USD'},
{value:200, name:'USD'},
{value:100, name:'USD'}];
var object1 = new Array;
objects1 = samount;
var categories1 = new Array();
var groupedObjects1 = [];
var output1 = '';
var i = 0;
console.log(samount);
_.each(objects1,function(obj){
var existingObj;
if($.inArray(obj.currency,categories1) >= 0) {
existingObj = _.find(objects1,function(o){return o.currency === obj.currency;});
existingObj.value += obj.value;
} else {
groupedObjects1[i] = obj;
categories1[i] = obj.currency;
i++;
}
});
console.log(samount);
console.log(groupedObjects1);
The problem is that I do not want that samount variable to change after looping, so I have done this:
var object1 = new Array;
objects1 = samount;
The goal of this script is to sum up all values from the same currencies, but still to not mess with the initial array.
But it still changes the initial Array. Could anyone help me with this error?
Copy the array with slice
var objects1 = samount.slice(0);
Arrays and object are passed by "reference" (not really, but doesn't matter here), so when assigning an array to a new variable, all you get is a reference to the same array, not a new array.
You need to deep copy the initial array instead of affecting it.
var samount = [{value:100, name:'USD'},
{value:200, name:'USD'},
{value:100, name:'USD'}];
var object1 = $.extend(true, [], samount);
You were doing an affectation (i.e. 2 variables pointing to the same object) where you needed a copy (2 variables pointing to 2 different objects)
The problem is you're not creating a copy with
objects1 = samount
In most OO languages, you can only copy primitive types so int, strings characters etc, but not objects.
This is somewhat similar in javascript in the sense that {} is an object, same as Array or [].
So if you want to copy an object you'd have to iterate over every element of that object till you find an primitive type. This can be tedious and quite hard even (http://andrewdupont.net/2009/08/28/deep-extending-objects-in-javascript/) this is called a deep copy.
But in this case a shallow copy (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/slice) is enough
var objects1 = samount.slice(0);
I am creating javascript two dimensional array
code is :
var field_arr=[];
$(".dr").each(function(index){
Id=$(this).attr("id");
alert(dragId);
topPos=$("#"+ dragId).position().top;
left=$("#"+ dragId).position().left;
parentDiv=$("#"+dragId).parent().attr("id");
parentDiv= parentDiv.split('-');
paId=parentDiv[1];
field_arr[Id]=new Array();
field_arr[Id]['paId']=paId;
field_arr[Id]['top']=topPos;
field_arr[Id]['left']=left;
});
console.log(field_arr);
Output Is:
[undefined, [] left 140 paId "1" top 10
What is problem in It Any help Should be appreciated.
The problem is in the display method of your arrays. The information is there, but both alert and console.log will not show it to you because it is expected that the only interesting properties of arrays are the ones with numeric indexes.
In JavaScript, unlike PHP, objects are used as maps/associative arrays.
First to check that your information is actually there:
$(".dr").each(function(index){
var Id=$(this).attr("id");
console.log(Id, field_arr[Id]['paId'], field_arr[Id]['top'], field_arr[Id]['left']);
});
Now to make make the display methods work you can go about multiple ways, but the best one is to use objects instead:
var field_arr = Object.create(null); // replace with {} if you want to support IE8-
$(".dr").each(function(index){
var id = $(this).attr("id"); // added var to keep variable local
var drag = $("#"+dragId);
field_arr[id] = Object.create(null); // {}
field_arr[id]['paId'] = drag.parent().attr("id").split('-')[1];
field_arr[id]['top'] = drag.position().top;
field_arr[id]['left'] = drag.position().left;
});
console.log(field_arr);
Iterating over properties of objects is quite easy:
for (var id in field_arr) {
console.log(field_arr[id], field_arr[id]['paId'], 'etc');
}
Add a hasOwnProperty check if your object doesn't inherit from null (var obj = {} needs it, unlike var obj = Object.create(null))
you're storing values with a key string and its wrong because you declared your field_arr as a numerical array (well there's no such thing as associative array in javascript i think).
field_arr[Id] = new Array();
field_arr[Id]['paId']=paId; //this is wrong
You need to create an object to store in values as if they are associated with string keys. But literally they are object properties
redeclare it like this
field_arr[Id] = {}; //you create an object
field_arr[Id]['paId'] = paId; //create an object property named paId and store a value
field_arr[Id].paId = paId; //you can also access property paId like this
EDIT:
but to conform to you current code you can access your indexes using strings by accessing it like a property of an object. (Thanks to Tibos)
var field_arr=[];
...
...
field_arr[Id].paId = paId;
I've got something like that:
var valueToPush = new Array();
valueToPush["productID"] = productID;
valueToPush["itemColorTitle"] = itemColorTitle;
valueToPush["itemColorPath"] = itemColorPath;
cookie_value_add.push(valueToPush);
the result is [];
what am i do wrong?
Arrays must have zero based integer indexes in JavaScript. So:
var valueToPush = new Array();
valueToPush[0] = productID;
valueToPush[1] = itemColorTitle;
valueToPush[2] = itemColorPath;
cookie_value_add.push(valueToPush);
Or maybe you want to use objects (which are associative arrays):
var valueToPush = { }; // or "var valueToPush = new Object();" which is the same
valueToPush["productID"] = productID;
valueToPush["itemColorTitle"] = itemColorTitle;
valueToPush["itemColorPath"] = itemColorPath;
cookie_value_add.push(valueToPush);
which is equivalent to:
var valueToPush = { };
valueToPush.productID = productID;
valueToPush.itemColorTitle = itemColorTitle;
valueToPush.itemColorPath = itemColorPath;
cookie_value_add.push(valueToPush);
It's a really fundamental and crucial difference between JavaScript arrays and JavaScript objects (which are associative arrays) that every JavaScript developer must understand.
Use []:
cookie_value_add.push([productID,itemColorTitle, itemColorPath]);
or
arrayToPush.push([value1, value2, ..., valueN]);
In JavaScript, the type of key/value store you are attempting to use is an object literal, rather than an array. You are mistakenly creating a composite array object, which happens to have other properties based on the key names you provided, but the array portion contains no elements.
Instead, declare valueToPush as an object and push that onto cookie_value_add:
// Create valueToPush as an object {} rather than an array []
var valueToPush = {};
// Add the properties to your object
// Note, you could also use the valueToPush["productID"] syntax you had
// above, but this is a more object-like syntax
valueToPush.productID = productID;
valueToPush.itemColorTitle = itemColorTitle;
valueToPush.itemColorPath = itemColorPath;
cookie_value_add.push(valueToPush);
// View the structure of cookie_value_add
console.dir(cookie_value_add);