---
id: 5d79253358e8f646cbeb2bb0
title: Part 15
challengeType: 0
isHidden: true
---
## Description
Change the `"+"` in the call to `infixToFunction` to `fn`.
`fn` is the operator that the user inputs (`+`, `-`, `*` or `/`) - we use `infixToFunction` to get the function that corresponds to it.
## Instructions
## Tests
```yml
tests:
- text: See description above for instructions.
testString: assert(code.replace(/\s/g, "").includes('str.replace(regex,(match,arg1,fn,arg2)=>infixToFunction[fn])'));
```
## Challenge Seed
```html
```
### Before Test
### After Test
```html
```
## Solution