---
id: 587d7b89367417b2b2512b48
title: Use the Spread Operator to Evaluate Arrays In-Place
challengeType: 1
---
## Description
ES6 introduces the spread operator, which allows us to expand arrays and other expressions in places where multiple parameters or elements are expected.
The ES5 code below uses apply() to compute the maximum value in an array:
var arr = [6, 89, 3, 45];
var maximus = Math.max.apply(null, arr); // returns 89
We had to use Math.max.apply(null, arr) because Math.max(arr) returns NaN. Math.max() expects comma-separated arguments, but not an array.
The spread operator makes this syntax much better to read and maintain.
const arr = [6, 89, 3, 45];
const maximus = Math.max(...arr); // returns 89
...arr returns an unpacked array. In other words, it spreads the array.
However, the spread operator only works in-place, like in an argument to a function or in an array literal. The following code will not work:
const spreaded = ...arr; // will throw a syntax error
## Instructions
Copy all contents of arr1 into another array arr2 using the spread operator.
## Tests
```yml
tests:
- text: arr2 is correct copy of arr1.
testString: assert(arr2.every((v, i) => v === arr1[i]), 'arr2 is correct copy of arr1.');
- text: ... spread operator was used to duplicate arr1.
testString: getUserInput => assert(getUserInput('index').match(/\[\s*...arr1\s*\]/g),'... spread operator was used to duplicate arr1.');
- text: arr2 remains unchanged when arr1 is changed.
testString: assert((arr1, arr2) => {arr1.push('JUN'); return arr2.length < arr1.length},'arr2 remains unchanged when arr1 is changed.');
```
## Challenge Seed
```js
const arr1 = ['JAN', 'FEB', 'MAR', 'APR', 'MAY'];
let arr2;
(function() {
"use strict";
arr2 = []; // change this line
})();
console.log(arr2);
```
## Solution
```js
const arr1 = ['JAN', 'FEB', 'MAR', 'APR', 'MAY'];
let arr2;
(function() {
"use strict";
arr2 = [...arr1]; // change this line
})();
console.log(arr2);
```