---
id: 5d792533ed00e75d129e1b18
title: Part 13
challengeType: 0
isHidden: true
---
## Description
`replace` is a higher order function because it can take a function as argument (higher order functions can also return functions).
Pass the `+` function from `infixToFunction` to the `replace` method as the second argument.
This is how you would pass the `-` function:
```js
str.replace(regex, infixToFunction["-"])
```
## Instructions
## Tests
```yml
tests:
- text: See description above for instructions.
testString: assert(infixEval("ab", /(a)b/) === "aba");
```
## Challenge Seed
```html
```
### Before Test
### After Test
```html
```
## Solution