freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/combine-two-arrays-using-the-concat-method.md

---
id: 587d7da9367417b2b2512b66
title: Combine Two Arrays Using the concat Method
challengeType: 1
forumTopicId: 301229
dashedName: combine-two-arrays-using-the-concat-method
---

# --description--

<dfn>Concatenation</dfn> means to join items end to end. JavaScript offers the `concat` method for both strings and arrays that work in the same way. For arrays, the method is called on one, then another array is provided as the argument to `concat`, which is added to the end of the first array. It returns a new array and does not mutate either of the original arrays. Here's an example:

```js
[1, 2, 3].concat([4, 5, 6]);
// Returns a new array [1, 2, 3, 4, 5, 6]
```

# --instructions--

Use the `concat` method in the `nonMutatingConcat` function to concatenate `attach` to the end of `original`. The function should return the concatenated array.

# --hints--

Your code should use the `concat` method.

```js
assert(code.match(/\.concat/g));
```

The `first` array should not change.

```js
assert(JSON.stringify(first) === JSON.stringify([1, 2, 3]));
```

The `second` array should not change.

```js
assert(JSON.stringify(second) === JSON.stringify([4, 5]));
```

`nonMutatingConcat([1, 2, 3], [4, 5])` should return `[1, 2, 3, 4, 5]`.

```js
assert(
  JSON.stringify(nonMutatingConcat([1, 2, 3], [4, 5])) ===
    JSON.stringify([1, 2, 3, 4, 5])
);
```

# --seed--

## --seed-contents--

```js
function nonMutatingConcat(original, attach) {
  // Only change code below this line


  // Only change code above this line
}
var first = [1, 2, 3];
var second = [4, 5];
nonMutatingConcat(first, second);
```

# --solutions--

```js
function nonMutatingConcat(original, attach) {
  // Only change code below this line
  return original.concat(attach);
  // Only change code above this line
}
var first = [1, 2, 3];
var second = [4, 5];
nonMutatingConcat(first, second);
```