How to concat multiple array into single array

Question

How to concat all this array into a single array:

[Array(10), Array(10), Array(10), Array(10), Array(10), Array(10), Array(10), Array(2)]

Possible duplicate of [Merge/flatten an array of arrays in JavaScript?](https://stackoverflow.com/questions/10865025/merge-flatten-an-array-of-arrays-in-javascript) — Mohammad Usman, Mar 02 '18 at 10:02

gurvinder372 · Answer 1 · 2018-03-02T09:50:52.257

4

Use reduce and concat

var output = arr.reduce( (a, c) => a.concat(c), []); //assuming arr is the input array

Edit

As @TJ mentioned in his comment, that above solution will create some intermediate arrays along the way, you can try (concat without spread)

var output = [].concat.apply([], arr);

or

var output = Array.prototype.concat.apply([], arr); //avoiding usage of another unnecessary array `[]`

edited Mar 02 '18 at 09:50

answered Mar 02 '18 at 09:34

gurvinder372

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Producing unnecessary intermediate arrays along the way... :-) – T.J. Crowder Mar 02 '18 at 09:36
@T.J.Crowder *unnecessary intermediate arrays* True, Or `[].concat.apply([], arr)` would suffice – gurvinder372 Mar 02 '18 at 09:41
Or you could avoid that last unnecessary array [like this](https://stackoverflow.com/questions/49066319/how-to-concat-multiple-array-into-single-array/49066344?noredirect=1#comment85137775_49066381). – T.J. Crowder Mar 02 '18 at 09:46

Faly · Answer 2 · 2018-03-02T09:36:56.540

4

You can use ES6's spread:

var arrays = [[1, 2], [3, 4], [5, 6]];
var res = [].concat(...arrays);
console.log(res);

edited Mar 02 '18 at 09:36

answered Mar 02 '18 at 09:36

Faly

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Good thought making use of `concat`'s handling of multiple arguments. – T.J. Crowder Mar 02 '18 at 09:37
@Bikshu s (and lurkers): If you can't use spread, the above is effectively: `var res = Array.prototype.concat.apply([], arrays);` – T.J. Crowder Mar 02 '18 at 09:38

score 0 · Answer 3 · answered Mar 02 '18 at 09:35

var array1 = ['a', 'b', 'c'];
var array2 = ['d', 'e', 'f'];

console.log(array1.concat(array2));
// expected output: Array ["a", "b", "c", "d", "e", "f"]

If you have an array of array you can do like so :

let bigArray = new Array();

arrayOfArray.forEach((arr) => {
    bigArray.concat(arr);
});

How to concat multiple array into single array

3 Answers3