Javascript arrays not merging

Question

Javascript arrays are not merging:

var randomArr = [1,2,3];
var randomArr2 = [4,5,6];

console.log(randomArr + randomArr2); // "1,2,34,5,6"

I get the result : 1,2,34,5,6
Why is that?

I expected [1,2,3] + [4,5,6] = [1,2,3,4,5,6]

Or if you're looking to append, see [*how-to-append-something-to-an-array*](https://stackoverflow.com/questions/351409/how-to-append-something-to-an-array) — Obsidian Age, Jul 01 '19 at 23:19
neither answer my question. randomShit.push(randomShit2) gives [1,2,3,[4,5,6]] — SQUIGGER, Jul 01 '19 at 23:20
@SQUIGGER please read the community Code of Conduct. Your language and attitude are not helping either side. https://stackoverflow.com/conduct — tkore, Jul 01 '19 at 23:23

Jack Bashford · Answer 1 · 2019-07-01T23:23:05.777

1

You want concat.

var randomArr = [1, 2, 3];
var randomArr2 = [4, 5, 6];

const res = randomArr.concat(randomArr2);

console.log(res);

You could alternatively concatenate the arrays into an empty array - this solution is more modular and avoids nesting of concat calls.

var randomArr = [1, 2, 3];
var randomArr2 = [4, 5, 6];
var randomArr3 = [7, 8, 9];

const res = [].concat(randomArr, randomArr2, randomArr3);

console.log(res);

.as-console-wrapper { max-height: 100% !important; top: auto; }

edited Jul 01 '19 at 23:23

answered Jul 01 '19 at 23:20

Jack Bashford

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finally that's what i was looking for – SQUIGGER Jul 01 '19 at 23:22
No problem @SQUIGGER, always glad to help. – Jack Bashford Jul 01 '19 at 23:23
how about `Array.prototype.concat.apply([], arrays)`? – SQUIGGER Jul 01 '19 at 23:24
That'd also work @SQUIGGER. – Jack Bashford Jul 01 '19 at 23:28

score 1 · Answer 2 · edited Jul 02 '19 at 00:28

1

You should use .concat https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/concat

let randomArr = [1,2,3];
let randomArr2 = [4,5,6];
let resultArray = randomArr.concat(randomArr2);
console.log(resultArray);

edited Jul 02 '19 at 00:28

tkore

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answered Jul 01 '19 at 23:21

Alejandro

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score 1 · Answer 3 · answered Jul 01 '19 at 23:23

JavaScript doesn't support adding or appending Arrays in the way you're trying to. It converts them to Strings: "1,2,3" and "4,5,6" then appends the second to the first, thus "1,2,34,5,6".

You want to use Array.concat to merge the arrays:

var randomArr = [1,2,3];
var randomArr2 = [4,5,6];

console.log(randomArr.concat(randomArr2)); // [1,2,3,4,5,6]

score 1 · Answer 4 · answered Jul 01 '19 at 23:23

1

You can't concatinate ("merge") arrays by using a plus.

Use Array.prototype.concat():

console.log(randomStuff1.concat(randomStuff2))

Use the spread operator:

console.log([...randomStuff1, ...randomStuff2])

answered Jul 01 '19 at 23:23

lforst

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spread operator is the most elegant way it seems – SQUIGGER Jul 01 '19 at 23:29
It looks pretty but is quite slow and error prone. Use it with caution. – lforst Jul 02 '19 at 00:01

score 1 · Answer 5 · answered Jul 01 '19 at 23:24

1

what you're looking for is:

var randomArr = [1,2,3];
var randomArr2 = [4,5,6];

var randomResult =randomArr.concat(randomArr2)
console.log(randomResult);

answered Jul 01 '19 at 23:24

corrado4eyes

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Javascript arrays not merging

5 Answers5