I actually asked myself the same question at the start of this year. UPDATED with new test cases http://jsperf.com/array-push-vs-unshift-vs-direct-assignment/2
It appears that push is much faster in chrome, and about equal in FF. Also direct is faster in IE9, but I would be interested to see how it performs in IE10.
I would say that most developers would assume setting the length of the array, and then using direct assignment is faster, as is the case with most programming languages. But JavaScript is different. Javascript arrays aren't really arrays, they're just key/value maps just like all other JavaScript objects. So the pre-allocation is essentially falling on deaf ears.
Personally I prefer push (:
Is there a reason JavaScript developers don't use Array.push()? - Stack Overflow
javascript - How can I push an object into an array? - Stack Overflow
javascript - Copy array items into another array - Stack Overflow
javascript - Push multiple elements to array - Stack Overflow
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I actually asked myself the same question at the start of this year. UPDATED with new test cases http://jsperf.com/array-push-vs-unshift-vs-direct-assignment/2
It appears that push is much faster in chrome, and about equal in FF. Also direct is faster in IE9, but I would be interested to see how it performs in IE10.
I would say that most developers would assume setting the length of the array, and then using direct assignment is faster, as is the case with most programming languages. But JavaScript is different. Javascript arrays aren't really arrays, they're just key/value maps just like all other JavaScript objects. So the pre-allocation is essentially falling on deaf ears.
Personally I prefer push (:
I believe that it's mostly habit.
Some developers use it simply because it's the way they are used to do it, and haven't considered that push would be an alternative.
Some developers have learned once upon a time that one method is much faster than another, and haven't reviewed this in light of the recent performance improvements of the Javascript engines.
Personally I use push frequently. Most of the time readability and maintainability is more important than performance, at least when the performance impact is small enough. The performance tests posted in the answers here show that the performance difference between various methods isn't very big.
You have to create an object. Assign the values to the object. Then push it into the array:
var nietos = [];
var obj = {};
obj["01"] = nieto.label;
obj["02"] = nieto.value;
nietos.push(obj);
Create an array of object like this:
var nietos = [];
nietos.push({"01": nieto.label, "02": nieto.value});
return nietos;
First you create the object inside of the push method and then return the newly created array.
Use the concat function, like so:
var arrayA = [1, 2];
var arrayB = [3, 4];
var newArray = arrayA.concat(arrayB);
The value of newArray will be [1, 2, 3, 4] (arrayA and arrayB remain unchanged; concat creates and returns a new array for the result).
In ECMAScript 6, you can use the Spread syntax:
let arr1 = [0, 1, 2];
let arr2 = [3, 4, 5];
arr1.push(...arr2);
console.log(arr1)Spread syntax is available in all major browsers (that excludes IE11). For the current compatibility, see this (continuously updated) compatibility table.
However, see Jack Giffin's reply below for more comments on performance. It seems concat is still better and faster than the spread operator.
You can push multiple elements into an array in the following way
var a = [];
a.push(1, 2, 3);
console.log(a);Now in ECMAScript2015 (a.k.a. ES6), you can use the spread operator to append multiple items at once:
var arr = [1];
var newItems = [2, 3];
arr.push(...newItems);
console.log(arr);See Kangax's ES6 compatibility table to see what browsers are compatible
How to push an object in an Array
const animals = ['pigs', 'goats', 'sheep'];
animals.push({animal: 'cows'});
console.log(animals); // ["pigs", "goats", "sheep", { animal: "cows" }]
I think like this:
var CatTitle = ['Travel', 'Daily Needs','Food & Beverages','Lifestyle','Gadget & Entertainment','Others'];
var myObj = {Coupon exp : 'xxx', couponcode : 'xxx'};
var newObject = {};
var newArray = [];
var i;
for(i=0; i < CatTitle.length; i++) {
var dump = {
CatTitle[i]: myObj
}
newArray.push(dump);
}
newObject = newArray;
You've got your assignment backwards*. It should be:
(window.foo = window.foo || []).push('bar');
The || operator in JavaScript does not return a boolean value. If the left hand side is truthy, it returns the left hand side, otherwise it returns the right hand side.
a = a || [];
is equivalent to
a = a ? a : [];
So an alternative way of writing the above is:
(window.foo = window.foo ? window.foo : []).push('bar');
* see comments for details
2021 Update
@zzzzBov's helpful answer,
(window.foo = window.foo || []).push('bar');
can be further simplified using the new ||= operator, logical OR assignment1,
(window.foo ||= []).push('bar');
1 See tcs39/proposal-logical-assignment, currently in Stage 4, and supported by major browsers.