Javascript push array values into another array

Provided your arrays are not huge (see caveat below), you can use the push() method of the array to which you wish to append values. push() can take multiple parameters so you can use its apply() method to pass the array of values to be pushed as a list of function parameters. This has the advantage over using concat() of adding elements to the array in place rather than creating a new array.

However, it seems that for large arrays (of the order of 100,000 members or more), this trick can fail. For such arrays, using a loop is a better approach. See http://stackoverflow.com/a/17368101/96100 for details.

var newArray = [];
newArray.push.apply(newArray, dataArray1);
newArray.push.apply(newArray, dataArray2);

You might want to generalize this into a function:

function pushArray(arr, arr2) {
    arr.push.apply(arr, arr2);
}

... or add it to Array's prototype:

Array.prototype.pushArray = function(arr) {
    this.push.apply(this, arr);
};

var newArray = [];
newArray.pushArray(dataArray1);
newArray.pushArray(dataArray2);

... or emulate the original push() method by allowing multiple parameters using the fact that concat(), like push(), allows multiple parameters:

Array.prototype.pushArray = function() {
    this.push.apply(this, this.concat.apply([], arguments));
};

var newArray = [];
newArray.pushArray(dataArray1, dataArray2);

Here's a loop-based version of the last example, suitable for large arrays and all major browsers, including IE <= 8:

Array.prototype.pushArray = function() {
    var toPush = this.concat.apply([], arguments);
    for (var i = 0, len = toPush.length; i < len; ++i) {
        this.push(toPush[i]);
    }
};

I will add one more "future-proof" reply

In ECMAScript 6, you can use the spread operator:

var arr1 = [0, 1, 2];
var arr2 = [3, 4, 5];
arr1.push(...arr2);

Spread operator is not yet included in all major browsers. For the current compatibility, see this (continuously updated) compatibility table.

You can, however, use spread operator with Babel.js.

Found an elegant way from MDN

var vegetables = ['parsnip', 'potato'];
var moreVegs = ['celery', 'beetroot'];

// Merge the second array into the first one
// Equivalent to vegetables.push('celery', 'beetroot');
Array.prototype.push.apply(vegetables, moreVegs);

console.log(vegetables); // ['parsnip', 'potato', 'celery', 'beetroot']

Or you can use the spread operator feature of ES6:

let fruits = [ 'apple', 'banana'];
const moreFruits = [ 'orange', 'plum' ];

fruits.push(...moreFruits); // ["apple", "banana", "orange", "plum"]

var a=new Array('a','b','c');
var b=new Array('d','e','f');
var d=new Array('x','y','z');
var c=a.concat(b,d)

Does that solve your problem ?

The following seems simplest to me:

var newArray = dataArray1.slice();
newArray.push.apply(newArray, dataArray2);

As "push" takes a variable number of arguments, you can use the apply method of the push function to push all of the elements of another array. It constructs a call to push using its first argument ("newArray" here) as "this" and the elements of the array as the remaining arguments.

The slice in the first statement gets a copy of the first array, so you don't modify it.

With JavaScript ES6, you can use the ... operator as a spread operator which will essentially convert the array into values. Then, you can do something like this:

var myArray = [1,2,3,4,5];
var moreData = [6,7,8,9,10];

myArray = [
  ...myArray,
  ...moreData,
];

While the syntax is concise, I do not know how this works internally and what the performance implications are on large arrays.