Related
This question already has answers here:
How do I test for an empty JavaScript object?
(48 answers)
Closed 5 years ago.
What is the fastest way to check if an object is empty or not?
Is there a faster and better way than this:
function count_obj(obj){
var i = 0;
for(var key in obj){
++i;
}
return i;
}
For ECMAScript5 (not supported in all browsers yet though), you can use:
Object.keys(obj).length === 0
I'm assuming that by empty you mean "has no properties of its own".
// Speed up calls to hasOwnProperty
var hasOwnProperty = Object.prototype.hasOwnProperty;
function isEmpty(obj) {
// null and undefined are "empty"
if (obj == null) return true;
// Assume if it has a length property with a non-zero value
// that that property is correct.
if (obj.length > 0) return false;
if (obj.length === 0) return true;
// If it isn't an object at this point
// it is empty, but it can't be anything *but* empty
// Is it empty? Depends on your application.
if (typeof obj !== "object") return true;
// Otherwise, does it have any properties of its own?
// Note that this doesn't handle
// toString and valueOf enumeration bugs in IE < 9
for (var key in obj) {
if (hasOwnProperty.call(obj, key)) return false;
}
return true;
}
Examples:
isEmpty(""), // true
isEmpty(33), // true (arguably could be a TypeError)
isEmpty([]), // true
isEmpty({}), // true
isEmpty({length: 0, custom_property: []}), // true
isEmpty("Hello"), // false
isEmpty([1,2,3]), // false
isEmpty({test: 1}), // false
isEmpty({length: 3, custom_property: [1,2,3]}) // false
If you only need to handle ECMAScript5 browsers, you can use Object.getOwnPropertyNames instead of the hasOwnProperty loop:
if (Object.getOwnPropertyNames(obj).length > 0) return false;
This will ensure that even if the object only has non-enumerable properties isEmpty will still give you the correct results.
EDIT: Note that you should probably use ES5 solution instead of this since ES5 support is widespread these days. It still works for jQuery though.
Easy and cross-browser way is by using jQuery.isEmptyObject:
if ($.isEmptyObject(obj))
{
// do something
}
More: http://api.jquery.com/jQuery.isEmptyObject/
You need jquery though.
Underscore and lodash each have a convenient isEmpty() function, if you don't mind adding an extra library.
_.isEmpty({});
Lets put this baby to bed; tested under Node, Chrome, Firefox and IE 9, it becomes evident that for most use cases:
(for...in...) is the fastest option to use!
Object.keys(obj).length is 10 times slower for empty objects
JSON.stringify(obj).length is always the slowest (not surprising)
Object.getOwnPropertyNames(obj).length takes longer than Object.keys(obj).length can be much longer on some systems.
Bottom line performance wise, use:
function isEmpty(obj) {
for (var x in obj) { return false; }
return true;
}
or
function isEmpty(obj) {
for (var x in obj) { if (obj.hasOwnProperty(x)) return false; }
return true;
}
Results under Node:
first result: return (Object.keys(obj).length === 0)
second result: for (var x in obj) { return false; }...
third result: for (var x in obj) { if (obj.hasOwnProperty(x)) return false; }...
forth result: return ('{}' === JSON.stringify(obj))
Testing for Object with 0 keys
0.00018
0.000015
0.000015
0.000324
Testing for Object with 1 keys
0.000346
0.000458
0.000577
0.000657
Testing for Object with 2 keys
0.000375
0.00046
0.000565
0.000773
Testing for Object with 3 keys
0.000406
0.000476
0.000577
0.000904
Testing for Object with 4 keys
0.000435
0.000487
0.000589
0.001031
Testing for Object with 5 keys
0.000465
0.000501
0.000604
0.001148
Testing for Object with 6 keys
0.000492
0.000511
0.000618
0.001269
Testing for Object with 7 keys
0.000528
0.000527
0.000637
0.00138
Testing for Object with 8 keys
0.000565
0.000538
0.000647
0.00159
Testing for Object with 100 keys
0.003718
0.00243
0.002535
0.01381
Testing for Object with 1000 keys
0.0337
0.0193
0.0194
0.1337
Note that if your typical use case tests a non empty object with few keys, and rarely do you get to test empty objects or objects with 10 or more keys, consider the Object.keys(obj).length option. - otherwise go with the more generic (for... in...) implementation.
Note that Firefox seem to have a faster support for Object.keys(obj).length and Object.getOwnPropertyNames(obj).length, making it a better choice for any non empty Object, but still when it comes to empty objects, the (for...in...) is simply 10 times faster.
My 2 cents is that Object.keys(obj).length is a poor idea since it creates an object of keys just to count how many keys are inside, than destroys it! In order to create that object he needs to loop overt the keys... so why use it and not the (for... in...) option :)
var a = {};
function timeit(func,count) {
if (!count) count = 100000;
var start = Date.now();
for (i=0;i<count;i++) func();
var end = Date.now();
var duration = end - start;
console.log(duration/count)
}
function isEmpty1() {
return (Object.keys(a).length === 0)
}
function isEmpty2() {
for (x in a) { return false; }
return true;
}
function isEmpty3() {
for (x in a) { if (a.hasOwnProperty(x)) return false; }
return true;
}
function isEmpty4() {
return ('{}' === JSON.stringify(a))
}
for (var j=0;j<10;j++) {
a = {}
for (var i=0;i<j;i++) a[i] = i;
console.log('Testing for Object with '+Object.keys(a).length+' keys')
timeit(isEmpty1);
timeit(isEmpty2);
timeit(isEmpty3);
timeit(isEmpty4);
}
a = {}
for (var i=0;i<100;i++) a[i] = i;
console.log('Testing for Object with '+Object.keys(a).length+' keys')
timeit(isEmpty1);
timeit(isEmpty2);
timeit(isEmpty3);
timeit(isEmpty4, 10000);
a = {}
for (var i=0;i<1000;i++) a[i] = i;
console.log('Testing for Object with '+Object.keys(a).length+' keys')
timeit(isEmpty1,10000);
timeit(isEmpty2,10000);
timeit(isEmpty3,10000);
timeit(isEmpty4,10000);
Elegant way - use keys
var myEmptyObj = {};
var myFullObj = {"key":"value"};
console.log(Object.keys(myEmptyObj).length); //0
console.log(Object.keys(myFullObj).length); //1
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys
function isEmpty( o ) {
for ( var p in o ) {
if ( o.hasOwnProperty( p ) ) { return false; }
}
return true;
}
var x= {}
var y= {x:'hi'}
console.log(Object.keys(x).length===0)
console.log(Object.keys(y).length===0)
true
false
http://jsfiddle.net/j7ona6hz/1/
Surprised to see so many weak answers on such a basic JS question... The top answer is no good too for these reasons:
it generates a global variable
returns true on undefined
uses for...in which is extremely slow by itself
function inside for...in is useless - return false without hasOwnProperty magic will work fine
In fact there's a simpler solution:
function isEmpty(value) {
return Boolean(value && typeof value === 'object') && !Object.keys(value).length;
}
https://lodash.com/docs#isEmpty comes in pretty handy:
_.isEmpty({}) // true
_.isEmpty() // true
_.isEmpty(null) // true
_.isEmpty("") // true
How bad is this?
function(obj){
for(var key in obj){
return false; // not empty
}
return true; // empty
}
No need for a library.
function(){ //must be within a function
var obj = {}; //the object to test
for(var isNotEmpty in obj) //will loop through once if there is a property of some sort, then
return alert('not empty')//what ever you are trying to do once
return alert('empty'); //nope obj was empty do this instead;
}
It might be a bit hacky. You can try this.
if (JSON.stringify(data).length === 2) {
// Do something
}
Not sure if there is any disadvantage of this method.
fast onliner for 'dictionary'-objects:
function isEmptyDict(d){for (var k in d) return false; return true}
You can write a fallback if Array.isArray and Object.getOwnPropertyNames is not available
XX.isEmpty = function(a){
if(Array.isArray(a)){
return (a.length==0);
}
if(!a){
return true;
}
if(a instanceof Object){
if(a instanceof Date){
return false;
}
if(Object.getOwnPropertyNames(a).length == 0){
return true;
}
}
return false;
}
Imagine you have the objects below:
var obj1= {};
var obj2= {test: "test"};
Don't forget we can NOT use === sign for testing an object equality as they get inheritance, so If you using ECMA 5 and upper version of javascript, the answer is easy, you can use the function below:
function isEmpty(obj) {
//check if it's an Obj first
var isObj = obj !== null
&& typeof obj === 'object'
&& Object.prototype.toString.call(obj) === '[object Object]';
if (isObj) {
for (var o in obj) {
if (obj.hasOwnProperty(o)) {
return false;
break;
}
}
return true;
} else {
console.error("isEmpty function only accept an Object");
}
}
so the result as below:
isEmpty(obj1); //this returns true
isEmpty(obj2); //this returns false
isEmpty([]); // log in console: isEmpty function only accept an Object
funtion isEmpty(o,i)
{
for(i in o)
{
return!1
}
return!0
}
here's a good way to do it
function isEmpty(obj) {
if (Array.isArray(obj)) {
return obj.length === 0;
} else if (typeof obj === 'object') {
for (var i in obj) {
return false;
}
return true;
} else {
return !obj;
}
}
var hasOwnProperty = Object.prototype.hasOwnProperty;
function isArray(a) {
return Object.prototype.toString.call(a) === '[object Array]'
}
function isObject(a) {
return Object.prototype.toString.call(a) === '[object Object]'
}
function isEmpty(a) {
if (null == a || "" == a)return!0;
if ("number" == typeof a || "string" == typeof a)return!1;
var b = !0;
if (isArray(a)) {
if (!a.length)return!0;
for (var c = 0; c < a.length; c++)isEmpty(a[c]) || (b = !1);
return b
}
if (isObject(a)) {
for (var d in a)hasOwnProperty.call(a, d) && (isEmpty(a[d]) || (b = !1));
return b
}
return!0
}
May be you can use this decision:
var isEmpty = function(obj) {
for (var key in obj)
if(obj.hasOwnProperty(key))
return false;
return true;
}
I modified Sean Vieira's code to suit my needs. null and undefined don't count as object at all, and numbers, boolean values and empty strings return false.
'use strict';
// Speed up calls to hasOwnProperty
var hasOwnProperty = Object.prototype.hasOwnProperty;
var isObjectEmpty = function(obj) {
// null and undefined are not empty
if (obj == null) return false;
if(obj === false) return false;
if(obj === true) return false;
if(obj === "") return false;
if(typeof obj === "number") {
return false;
}
// Assume if it has a length property with a non-zero value
// that that property is correct.
if (obj.length > 0) return false;
if (obj.length === 0) return true;
// Otherwise, does it have any properties of its own?
// Note that this doesn't handle
// toString and valueOf enumeration bugs in IE < 9
for (var key in obj) {
if (hasOwnProperty.call(obj, key)) return false;
}
return true;
};
exports.isObjectEmpty = isObjectEmpty;
here my solution
function isEmpty(value) {
if(Object.prototype.toString.call(value) === '[object Array]') {
return value.length == 0;
} else if(value != null && typeof value === 'object') {
return Object.getOwnPropertyNames(value).length == 0;
} else {
return !(value || (value === 0));
}
}
Chears
if (Object.getOwnPropertyNames(obj1).length > 0)
{
alert('obj1 is empty!');
}
How can i replace find method. It is used incorrectly. IE don't see var mail.
var mail = textObj.products.find(function ( itm ) { return itm.name == c }).mail
Array.prototype.find() is not yet supported in IE and Opera (source).
If you want to use it, you should insert the Polyfill function for it:
if (!Array.prototype.find) {
Array.prototype.find = function(predicate) {
if (this === null) {
throw new TypeError('Array.prototype.find called on null or undefined');
}
if (typeof predicate !== 'function') {
throw new TypeError('predicate must be a function');
}
var list = Object(this);
var length = list.length >>> 0;
var thisArg = arguments[1];
var value;
for (var i = 0; i < length; i++) {
value = list[i];
if (predicate.call(thisArg, value, i, list)) {
return value;
}
}
return undefined;
};
}
Alternatively, you can use the Array.prototype.filter() function , which is available in IE9 (and up).
This is experimental technology and is not supported by every browser. You should use filter instead:
textObj.products.filter(function ( itm ) { return itm.name == c })[0].mail
This question already has answers here:
Test for existence of nested JavaScript object key
(64 answers)
Closed 5 years ago.
I'm trying to find an elegant way to check the if certain deep properties exist in an object. So practically trying to avoid monstrous protective checks for undefined eg.
if ((typeof error !== 'undefined') &&
(typeof error.responseJSON !== 'undefined') &&
(typeof error.responseJSON.error) &&
(typeof error.responseJSON.error.message)) {
errorMessage = error.responseJSON.error.message;
}
What I'm thinking about is a convenience-function like
if (exists(error.responseJSON.error.message)) { ... }
Any ideas? For convenience, the use of underscore-library is ok for the solution.
There are several possiblities:
Try-catch
try {
errorMessage = error.responseJSON.error.message;
} catch(e) { /* ignore the error */}
Fails for:
Object.defineProperty(error, 'responseJSON', {
get: function() { throw new Error('This will not be shown')
});
&&
errorMessage = error && error.responseJSON && error.responseJSON.error && error.responseJSON.error.message;
Fails for:
error.responseJSON = 0;
// errorMessage === 0 instead of undefined
function
function getDeepProperty(obj,propstr) {
var prop = propstr.split('.');
for (var i=0; i<prop.length; i++) {
if (typeof obj === 'object')
obj = obj[prop[i]];
}
return obj;
}
errorMessage = getDeepProperty(error, 'responseJSON.error.message');
// you could put it all in a string, if the object is defined in the window scope
Fails for:
// It's hard(er) to use
function alternative - see comment by #Olical
function getDeepProperty(obj) {
for (var i=1; i<arguments.length; i++) {
if (typeof obj === 'object')
obj = obj[arguments[i]];
}
return obj;
}
errorMessage = getDeepProperty(error, 'responseJSON', 'error', 'message');
Try this underscore mixin to look up a variable with a path. It takes an object and string and t
_.mixin({
lookup: function (obj, key) {
var type = typeof key;
if (type == 'string' || type == "number")
key = ("" + key).replace(/\[(.*?)\]/, function (m, key) { //handle case where [1] may occur
return '.' + key.replace(/["']/g, ""); //strip quotes
}).split('.');
for (var i = 0, l = key.length; i < l; i++) {
if (_.has(obj, key[i]))
obj = obj[key[i]];
else
return undefined;
}
return obj;
}
});
Now call in your example:
_.lookup(error, 'responseJSON.error.message') // returns responseJSON.error.message if it exists otherwise `undefined`
This question already has answers here:
How do I test for an empty JavaScript object?
(48 answers)
Closed 5 years ago.
What is the fastest way to check if an object is empty or not?
Is there a faster and better way than this:
function count_obj(obj){
var i = 0;
for(var key in obj){
++i;
}
return i;
}
For ECMAScript5 (not supported in all browsers yet though), you can use:
Object.keys(obj).length === 0
I'm assuming that by empty you mean "has no properties of its own".
// Speed up calls to hasOwnProperty
var hasOwnProperty = Object.prototype.hasOwnProperty;
function isEmpty(obj) {
// null and undefined are "empty"
if (obj == null) return true;
// Assume if it has a length property with a non-zero value
// that that property is correct.
if (obj.length > 0) return false;
if (obj.length === 0) return true;
// If it isn't an object at this point
// it is empty, but it can't be anything *but* empty
// Is it empty? Depends on your application.
if (typeof obj !== "object") return true;
// Otherwise, does it have any properties of its own?
// Note that this doesn't handle
// toString and valueOf enumeration bugs in IE < 9
for (var key in obj) {
if (hasOwnProperty.call(obj, key)) return false;
}
return true;
}
Examples:
isEmpty(""), // true
isEmpty(33), // true (arguably could be a TypeError)
isEmpty([]), // true
isEmpty({}), // true
isEmpty({length: 0, custom_property: []}), // true
isEmpty("Hello"), // false
isEmpty([1,2,3]), // false
isEmpty({test: 1}), // false
isEmpty({length: 3, custom_property: [1,2,3]}) // false
If you only need to handle ECMAScript5 browsers, you can use Object.getOwnPropertyNames instead of the hasOwnProperty loop:
if (Object.getOwnPropertyNames(obj).length > 0) return false;
This will ensure that even if the object only has non-enumerable properties isEmpty will still give you the correct results.
EDIT: Note that you should probably use ES5 solution instead of this since ES5 support is widespread these days. It still works for jQuery though.
Easy and cross-browser way is by using jQuery.isEmptyObject:
if ($.isEmptyObject(obj))
{
// do something
}
More: http://api.jquery.com/jQuery.isEmptyObject/
You need jquery though.
Underscore and lodash each have a convenient isEmpty() function, if you don't mind adding an extra library.
_.isEmpty({});
Lets put this baby to bed; tested under Node, Chrome, Firefox and IE 9, it becomes evident that for most use cases:
(for...in...) is the fastest option to use!
Object.keys(obj).length is 10 times slower for empty objects
JSON.stringify(obj).length is always the slowest (not surprising)
Object.getOwnPropertyNames(obj).length takes longer than Object.keys(obj).length can be much longer on some systems.
Bottom line performance wise, use:
function isEmpty(obj) {
for (var x in obj) { return false; }
return true;
}
or
function isEmpty(obj) {
for (var x in obj) { if (obj.hasOwnProperty(x)) return false; }
return true;
}
Results under Node:
first result: return (Object.keys(obj).length === 0)
second result: for (var x in obj) { return false; }...
third result: for (var x in obj) { if (obj.hasOwnProperty(x)) return false; }...
forth result: return ('{}' === JSON.stringify(obj))
Testing for Object with 0 keys
0.00018
0.000015
0.000015
0.000324
Testing for Object with 1 keys
0.000346
0.000458
0.000577
0.000657
Testing for Object with 2 keys
0.000375
0.00046
0.000565
0.000773
Testing for Object with 3 keys
0.000406
0.000476
0.000577
0.000904
Testing for Object with 4 keys
0.000435
0.000487
0.000589
0.001031
Testing for Object with 5 keys
0.000465
0.000501
0.000604
0.001148
Testing for Object with 6 keys
0.000492
0.000511
0.000618
0.001269
Testing for Object with 7 keys
0.000528
0.000527
0.000637
0.00138
Testing for Object with 8 keys
0.000565
0.000538
0.000647
0.00159
Testing for Object with 100 keys
0.003718
0.00243
0.002535
0.01381
Testing for Object with 1000 keys
0.0337
0.0193
0.0194
0.1337
Note that if your typical use case tests a non empty object with few keys, and rarely do you get to test empty objects or objects with 10 or more keys, consider the Object.keys(obj).length option. - otherwise go with the more generic (for... in...) implementation.
Note that Firefox seem to have a faster support for Object.keys(obj).length and Object.getOwnPropertyNames(obj).length, making it a better choice for any non empty Object, but still when it comes to empty objects, the (for...in...) is simply 10 times faster.
My 2 cents is that Object.keys(obj).length is a poor idea since it creates an object of keys just to count how many keys are inside, than destroys it! In order to create that object he needs to loop overt the keys... so why use it and not the (for... in...) option :)
var a = {};
function timeit(func,count) {
if (!count) count = 100000;
var start = Date.now();
for (i=0;i<count;i++) func();
var end = Date.now();
var duration = end - start;
console.log(duration/count)
}
function isEmpty1() {
return (Object.keys(a).length === 0)
}
function isEmpty2() {
for (x in a) { return false; }
return true;
}
function isEmpty3() {
for (x in a) { if (a.hasOwnProperty(x)) return false; }
return true;
}
function isEmpty4() {
return ('{}' === JSON.stringify(a))
}
for (var j=0;j<10;j++) {
a = {}
for (var i=0;i<j;i++) a[i] = i;
console.log('Testing for Object with '+Object.keys(a).length+' keys')
timeit(isEmpty1);
timeit(isEmpty2);
timeit(isEmpty3);
timeit(isEmpty4);
}
a = {}
for (var i=0;i<100;i++) a[i] = i;
console.log('Testing for Object with '+Object.keys(a).length+' keys')
timeit(isEmpty1);
timeit(isEmpty2);
timeit(isEmpty3);
timeit(isEmpty4, 10000);
a = {}
for (var i=0;i<1000;i++) a[i] = i;
console.log('Testing for Object with '+Object.keys(a).length+' keys')
timeit(isEmpty1,10000);
timeit(isEmpty2,10000);
timeit(isEmpty3,10000);
timeit(isEmpty4,10000);
Elegant way - use keys
var myEmptyObj = {};
var myFullObj = {"key":"value"};
console.log(Object.keys(myEmptyObj).length); //0
console.log(Object.keys(myFullObj).length); //1
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys
function isEmpty( o ) {
for ( var p in o ) {
if ( o.hasOwnProperty( p ) ) { return false; }
}
return true;
}
var x= {}
var y= {x:'hi'}
console.log(Object.keys(x).length===0)
console.log(Object.keys(y).length===0)
true
false
http://jsfiddle.net/j7ona6hz/1/
Surprised to see so many weak answers on such a basic JS question... The top answer is no good too for these reasons:
it generates a global variable
returns true on undefined
uses for...in which is extremely slow by itself
function inside for...in is useless - return false without hasOwnProperty magic will work fine
In fact there's a simpler solution:
function isEmpty(value) {
return Boolean(value && typeof value === 'object') && !Object.keys(value).length;
}
https://lodash.com/docs#isEmpty comes in pretty handy:
_.isEmpty({}) // true
_.isEmpty() // true
_.isEmpty(null) // true
_.isEmpty("") // true
How bad is this?
function(obj){
for(var key in obj){
return false; // not empty
}
return true; // empty
}
No need for a library.
function(){ //must be within a function
var obj = {}; //the object to test
for(var isNotEmpty in obj) //will loop through once if there is a property of some sort, then
return alert('not empty')//what ever you are trying to do once
return alert('empty'); //nope obj was empty do this instead;
}
It might be a bit hacky. You can try this.
if (JSON.stringify(data).length === 2) {
// Do something
}
Not sure if there is any disadvantage of this method.
fast onliner for 'dictionary'-objects:
function isEmptyDict(d){for (var k in d) return false; return true}
You can write a fallback if Array.isArray and Object.getOwnPropertyNames is not available
XX.isEmpty = function(a){
if(Array.isArray(a)){
return (a.length==0);
}
if(!a){
return true;
}
if(a instanceof Object){
if(a instanceof Date){
return false;
}
if(Object.getOwnPropertyNames(a).length == 0){
return true;
}
}
return false;
}
Imagine you have the objects below:
var obj1= {};
var obj2= {test: "test"};
Don't forget we can NOT use === sign for testing an object equality as they get inheritance, so If you using ECMA 5 and upper version of javascript, the answer is easy, you can use the function below:
function isEmpty(obj) {
//check if it's an Obj first
var isObj = obj !== null
&& typeof obj === 'object'
&& Object.prototype.toString.call(obj) === '[object Object]';
if (isObj) {
for (var o in obj) {
if (obj.hasOwnProperty(o)) {
return false;
break;
}
}
return true;
} else {
console.error("isEmpty function only accept an Object");
}
}
so the result as below:
isEmpty(obj1); //this returns true
isEmpty(obj2); //this returns false
isEmpty([]); // log in console: isEmpty function only accept an Object
funtion isEmpty(o,i)
{
for(i in o)
{
return!1
}
return!0
}
here's a good way to do it
function isEmpty(obj) {
if (Array.isArray(obj)) {
return obj.length === 0;
} else if (typeof obj === 'object') {
for (var i in obj) {
return false;
}
return true;
} else {
return !obj;
}
}
var hasOwnProperty = Object.prototype.hasOwnProperty;
function isArray(a) {
return Object.prototype.toString.call(a) === '[object Array]'
}
function isObject(a) {
return Object.prototype.toString.call(a) === '[object Object]'
}
function isEmpty(a) {
if (null == a || "" == a)return!0;
if ("number" == typeof a || "string" == typeof a)return!1;
var b = !0;
if (isArray(a)) {
if (!a.length)return!0;
for (var c = 0; c < a.length; c++)isEmpty(a[c]) || (b = !1);
return b
}
if (isObject(a)) {
for (var d in a)hasOwnProperty.call(a, d) && (isEmpty(a[d]) || (b = !1));
return b
}
return!0
}
May be you can use this decision:
var isEmpty = function(obj) {
for (var key in obj)
if(obj.hasOwnProperty(key))
return false;
return true;
}
I modified Sean Vieira's code to suit my needs. null and undefined don't count as object at all, and numbers, boolean values and empty strings return false.
'use strict';
// Speed up calls to hasOwnProperty
var hasOwnProperty = Object.prototype.hasOwnProperty;
var isObjectEmpty = function(obj) {
// null and undefined are not empty
if (obj == null) return false;
if(obj === false) return false;
if(obj === true) return false;
if(obj === "") return false;
if(typeof obj === "number") {
return false;
}
// Assume if it has a length property with a non-zero value
// that that property is correct.
if (obj.length > 0) return false;
if (obj.length === 0) return true;
// Otherwise, does it have any properties of its own?
// Note that this doesn't handle
// toString and valueOf enumeration bugs in IE < 9
for (var key in obj) {
if (hasOwnProperty.call(obj, key)) return false;
}
return true;
};
exports.isObjectEmpty = isObjectEmpty;
here my solution
function isEmpty(value) {
if(Object.prototype.toString.call(value) === '[object Array]') {
return value.length == 0;
} else if(value != null && typeof value === 'object') {
return Object.getOwnPropertyNames(value).length == 0;
} else {
return !(value || (value === 0));
}
}
Chears
if (Object.getOwnPropertyNames(obj1).length > 0)
{
alert('obj1 is empty!');
}
Do you know a JavaScript library that implements a generic Iterator class for collections (be it Arrays or some abstract Enumerable) with a full set of features, like the Google Common or the Apache Commons?
Edit: Enumerable#each is not an Iterator class. I'm looking for an Iterator, something that would let us write something like:
var iterator = new Iterator(myCollection);
for (var element = iterator.next(); iterator.hasNext(); element = iterator.next()) {
// iterator
}
Edit : mamoo reminded us of the Iterator implementation in Mozilla's Javascript 1.7. So the goal now is to find an implementation of this Iterator function in Javascript 1.5 (ECMA 4).
Edit2 : Why using an iterator when libraries (and ECMA 5) provide a each method? First, because each usually messes with this because the callback is call -ed (that's why each accepts a second argument in Prototype). Then, because people are much more familiar with the for(;;) construct than with the .each(callback) construct (at least, in my field). Lastly, because an iterator can iterate over plain objects (see JavaScript 1.7).
Edit3 : I accepted npup's anwser, but here is my shot at it :
function Iterator(o, keysOnly) {
if (!(this instanceof arguments.callee))
return new arguments.callee(o, keysOnly);
var index = 0, keys = [];
if (!o || typeof o != "object") return;
if ('splice' in o && 'join' in o) {
while(keys.length < o.length) keys.push(keys.length);
} else {
for (p in o) if (o.hasOwnProperty(p)) keys.push(p);
}
this.next = function next() {
if (index < keys.length) {
var key = keys[index++];
return keysOnly ? key : [key, o[key]];
} else throw { name: "StopIteration" };
};
this.hasNext = function hasNext() {
return index < keys.length;
};
}
var lang = { name: 'JavaScript', birthYear: 1995 };
var it = Iterator(lang);
while (it.hasNext()) {
alert(it.next());
}
//alert(it.next()); // A StopIteration exception is thrown
var langs = ['JavaScript', 'Python', 'C++'];
var it = Iterator(langs);
while (it.hasNext()) {
alert(it.next());
}
//alert(it.next()); // A StopIteration exception is thrown
Ok, the enumerable pattern is not a real iterator then.
Is this (below) useful for you? It conforms to the sematics you gave at least. As usual there are tradeoffs to be made here and there, and I didn't think very hard when deciding this time :).
And maybe you would like to be able to send in a number or two and iterate over a range in that way. But this could maybe be a start (there's support for iterating over hashes, arrays and strings).
It's a whole demo page which runs itself and does some debug output, but the (possibly) interesting stuff is in the
window.npup = (function() {
[...]
})();
spot.
Maybe it is just me who doesn't get it at all, but what would you use such a java-like Iterator for in a real situation?
Best
/npup
<html>
<head>
<title>untitled</title>
</head>
<body>
<ul id="output"></ul>
<script type="text/javascript">
window.log = (function (outputAreaId) {
var myConsole = document.getElementById(outputAreaId);
function createElem(color) {
var elem = document.createElement('li');
elem.style.color = color;
return elem;
}
function appendElem(elem) {
myConsole.appendChild(elem);
}
function debug(msg) {
var elem = createElem('#888');
elem.innerHTML = msg;
appendElem(elem);
}
function error(msg) {
var elem = createElem('#f88');
elem.innerHTML = msg;
appendElem(elem);
}
return {
debug: debug
, error: error
};
})('output');
window.npup = (function () {
// Array check as proposed by Mr. Crockford
function isArray(candidate) {
return candidate &&
typeof candidate==='object' &&
typeof candidate.length === 'number' &&
typeof candidate.splice === 'function' &&
!(candidate.propertyIsEnumerable('length'));
}
function dontIterate(collection) {
// put some checks chere for stuff that isn't iterable (yet)
return (!collection || typeof collection==='number' || typeof collection==='boolean');
}
function Iterator(collection) {
if (typeof collection==='string') {collection = collection.split('');}
if (dontIterate(collection)) {throw new Error('Oh you nasty man, I won\'t iterate over that ('+collection+')!');}
var arr = isArray(collection);
var idx = 0, top=0;
var keys = [], prop;
if (arr) {top = collection.length;}
else {for (prop in collection) {keys.push(prop);}}
this.next = function () {
if (!this.hasNext()) {throw new Error('Oh you nasty man. I have no more elements.');}
var elem = arr ? collection[idx] : {key:keys[idx], value:collection[keys[idx]]};
++idx;
return elem;
};
this.hasNext = function () {return arr ? idx<=top : idx<=keys.length;};
}
return {Iterator: Iterator};
})();
var element;
log.debug('--- Hash demo');
var o = {foo:1, bar:2, baz:3, bork:4, hepp: {a:1,b:2,c:3}, bluff:666, bluff2:777};
var iterator = new npup.Iterator(o);
for (element = iterator.next(); iterator.hasNext(); element = iterator.next()) {
log.debug('got elem from hash: '+element.key+' => '+element.value);
if (typeof element.value==='object') {
var i2 = new npup.Iterator(element.value);
for (var e2=i2.next(); i2.hasNext(); e2=i2.next()) {
log.debug(' # from inner hash: '+e2.key+' => '+e2.value);
}
}
}
log.debug('--- Array demo');
var a = [1,2,3,42,666,777];
iterator = new npup.Iterator(a);
for (element = iterator.next(); iterator.hasNext(); element = iterator.next()) {
log.debug('got elem from array: '+ element);
}
log.debug('--- String demo');
var s = 'First the pants, THEN the shoes!';
iterator = new npup.Iterator(s);
for (element = iterator.next(); iterator.hasNext(); element = iterator.next()) {
log.debug('got elem from string: '+ element);
}
log.debug('--- Emptiness demo');
try {
log.debug('Try to get next..');
var boogie = iterator.next();
}
catch(e) {
log.error('OW: '+e);
}
log.debug('--- Non iterables demo');
try{iterator = new npup.Iterator(true);} catch(e) {log.error('iterate over boolean: '+e);}
try{iterator = new npup.Iterator(6);} catch(e) {log.error('iterate over number: '+e);}
try{iterator = new npup.Iterator(null);} catch(e) {log.error('iterate over null: '+e);}
try{iterator = new npup.Iterator();} catch(e) {log.error('iterate over undefined: '+e);}
</script>
</body>
</html>
JQuery has the each() method:
http://api.jquery.com/jQuery.each/
but probably there's something similar even in other libraries such as Moo or Dojo.
Javascript 1.7 implements the Iterator function:
https://developer.mozilla.org/en/Core_JavaScript_1.5_Guide/Iterators_and_Generators
This is my attempt (jsfiddle) for ECMAScript 262 5th edition (aka Javascript). (Uses for example Object.keys and Array.isArray)
//Usage
b=Iterator(a);
while(b()){
console.log(b.value);
}
The code:
function Iterator(input,keys) {
// Input:
// input : object|array
// keys : array|undefined|boolean
function my() {
++my.index;
if (my.index >= my.keys.length) {
my.index = my.keys.length -1;
my.key = my.value = undefined;
return false;
}
my.key = my.useIndex ? my.index : my.keys[my.index];
my.value = my.input[my.key];
return my.index < my.keys.length;
}
if (input === null || typeof input !== 'object') {
throw new TypeError("'input' should be object|array");
}
if (
!Array.isArray(keys)
&& (typeof keys !== 'undefined')
&& (typeof keys !== 'boolean')
) {
throw new TypeError("'keys' should be array|boolean|undefined");
}
// Save a reference to the input object.
my.input = input;
if (Array.isArray(input)) {
//If the input is an array, set 'useIndex' to true if
//the internal index should be used as a key.
my.useIndex = !keys;
//Either create and use a list of own properties,
// or use the supplied keys
// or at last resort use the input (since useIndex is true in that
// case it is only used for the length)
my.keys = keys===true ? Object.keys(input) : keys || input;
} else {
my.useIndex = false;
my.keys = Array.isArray(keys) ? keys : Object.keys(input);
}
// Set index to before the first element.
my.index = -1;
return my;
}
Examples:
function Person(firstname, lastname, domain) {
this.firstname = firstname;
this.lastname = lastname;
this.domain = domain;
}
Person.prototype.type = 'Brillant';
var list = [
new Person('Paula','Bean','some.domain.name'),
new Person('John','Doe','another.domain.name'),
new Person('Johanna','Doe','yet.another.domain.name'),
];
var a,b;
var data_array = ['A','B','C','D','E','F'];
data_array[10]="Sparse";
console.log('Iterate over own keys in an object, unknown order');
a = Iterator(list[0]);
while(a()) console.log(" ",a.key, a.value);
console.log('Iterate over keys from anywhere, in specified order');
a = Iterator(list[0], ['lastname','firstname','type']);
while(a()) console.log(" ",a.key, a.value);
console.log('Iterate over all values in an array');
a = Iterator(list);
while(a()) console.log(a.key, a.value.firstname, a.value.lastname);
//Some abusing, that works for arrays (if the iterator.keys is modified
//it can also be used for objects)
console.log('Add more entries to the array, reusing the iterator...');
list.push(new Person('Another','Name','m.nu'));
while(a()) console.log(a.key, a.value.firstname, a.value.lastname);
console.log('Reset index and print everything again...');
a.index=-1; //Reset the index.
while(a()) console.log(a.key, a.value.firstname, a.value.lastname);
//With arrays, if setting 'keys' to true it will only print the
//elements that has values (If the array has more own enumerable values
//they too will be included)
console.log('Print sparce arrays...');
a = Iterator(data_array,true);
while(a()) console.log(a.key, a.value);
In the time since this question was asked JavaScript has added actual Iterators. Some built-in types, such as Array, Map, and String now have a default iteration behavior, but you can add your own to any object by including a next() function which returns one of two objects:
{done:true} /*or*/
{done:false, value:SOMEVALUE}
One way to access an object Iterator is with the:
for ( var of object ) { }
loop. Here is a (reasonably silly) example where we define an Iterator and then use it in such a loop to produce a string 1, 2, 3:
"use strict";
function count ( i ) {
let n = 0;
let I = {};
I[Symbol.iterator] = function() {
return { next: function() { return (n > i) ? {done:true}
: {done:false, value:n++} } } };
let s = "";
let c = "";
for ( let i of I ) { /* use the iterator we defined above */
s += c + i;
c = ", "
}
return s;
}
let s = count(3);
console.log(s);
Ive used LINQ to Javascript in a few projects.
http://jslinq.codeplex.com/Wikipage
var myList = [
{FirstName:"Chris",LastName:"Pearson"},
{FirstName:"Kate",LastName:"Johnson"},
{FirstName:"Josh",LastName:"Sutherland"},
{FirstName:"John",LastName:"Ronald"},
{FirstName:"Steve",LastName:"Pinkerton"}
];
var exampleArray = JSLINQ(myList)
.Where(function(item){ return item.FirstName == "Chris"; })
.OrderBy(function(item) { return item.FirstName; })
.Select(function(item){ return item.FirstName; });
I'm still a learner of js.class.
Though being close to Ruby, helps me.
http://jsclass.jcoglan.com/enumerable.html
MarkT
Since this hasn't been mention yet arrays have higher-order functions built in.
Map works like iterator that can only do a single pass.
[1,2,3,4,5].map( function(input){ console.log(input); } );
This code passes each element in the list into a function, in this case its a simple printer.
1
2
3
4
5