--- id: 5d7925341747ad42b12f8e68 title: Part 42 challengeType: 0 isHidden: true --- ## Description
This is still valid because we're modifying `arr` in place instead of reassigning to it (which is invalid with the `const` keyword). But doing this still modifies state, and we don't want to do that in functional programming. The `concat` method returns a new array instead of modifying an existing one: ```js [1,2,3].concat(4); // [1, 2, 3, 4] [1,2,3].concat(4, 5); // [1, 2, 3, 4, 5] ``` Use `concat` instead of `push` to return the result of adding `end` to `arr`.
## Instructions
## Tests
```yml tests: - text: See description above for instructions. testString: assert(JSON.stringify(range(1,2)) === "[1,2]" && code.includes("concat") && !(code.includes("push"))); ```
## Challenge Seed
```html ```
### Before Test
```html Spreadsheet
```
### After Test
```html ```
## Solution
```html ```