Question

198

What is the equivalent of Java `Collection.addAll` for JavaScript arrays?

rated 0 times [ 200] [ 2] / answers: 1 / hits: 39590 / 8 Years ago, fri, february 26, 2016, 12:00:00

Java Collections have a method to add all elements of another collection: addAll(Collection other).

What is the equivalent to do in place appending of javascript arrays?

We cannot use Array.concat, because it creates a new array and leaves the original array untouched.

So, given two arrays, how b to a, how to append all elements of b to a in place (therefore c also changes!):

var a = [1, 2, 3];

var b = ['foo', 'bar'];

var c = a;

// a.addAll(b);

// so that `c` equals to  [1, 2, 3, 'foo', 'bar']

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answered 8 Years ago katharinek · Accepted Answer

You can use the apply method of Array.prototype.push():

var a = [1, 2, 3];

var b = ['foo', 'bar'];

Array.prototype.push.apply(a, b);

console.log(a); // Array [ 1, 2, 3, foo, bar ]

or alternatively:

a.push.apply(a, b);

[].push.apply(a, b);

If you're using ES6, it's better to call .push() using the spread operator ... instead. This is more similar to Collection.addAll(...) because you can add values from any iterable object, not just arrays. It also allows you to add multiple iterables at once.

const a = [1, 2, 3];

const b = ['foo', 'bar'];

const c = new Set(['x', 'x', 'y', 'x']);

a.push(...b, ...c);

console.log(a); // Array [ 1, 2, 3, foo, bar, x, y ]