freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/es6/write-arrow-functions-with-parameters.md

---
id: 587d7b88367417b2b2512b44
title: Write Arrow Functions with Parameters
challengeType: 1
forumTopicId: 301223
---

# --description--

Just like a regular function, you can pass arguments into an arrow function.

```js
// doubles input value and returns it
const doubler = (item) => item * 2;
doubler(4); // returns 8
```

If an arrow function has a single parameter, the parentheses enclosing the parameter may be omitted.

```js
// the same function, without the parameter parentheses
const doubler = item => item * 2;
```

It is possible to pass more than one argument into an arrow function.

```js
// multiplies the first input value by the second and returns it
const multiplier = (item, multi) => item * multi;
multiplier(4, 2); // returns 8
```

# --instructions--

Rewrite the `myConcat` function which appends contents of `arr2` to `arr1` so that the function uses arrow function syntax.

# --hints--

You should replace the `var` keyword.

```js
(getUserInput) => assert(!getUserInput('index').match(/var/g));
```

`myConcat` should be a constant variable (by using `const`).

```js
(getUserInput) => assert(getUserInput('index').match(/const\s+myConcat/g));
```

`myConcat` should be an arrow function with two parameters

```js
assert(
  /myConcat=\(\w+,\w+\)=>/.test(code.replace(/\s/g, '')) &&
    typeof myConcat === 'function'
);
```

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

```js
assert.deepEqual(myConcat([1, 2], [3, 4, 5]), [1, 2, 3, 4, 5]);
```

`function` keyword should not be used.

```js
(getUserInput) => assert(!getUserInput('index').match(/function/g));
```

# --seed--

## --seed-contents--

```js
var myConcat = function(arr1, arr2) {
  return arr1.concat(arr2);
};

console.log(myConcat([1, 2], [3, 4, 5]));
```

# --solutions--

```js
const myConcat = (arr1, arr2) =>  {
  return arr1.concat(arr2);
};

console.log(myConcat([1, 2], [3, 4, 5]));
```