---
id: 587d7b8c367417b2b2512b58
title: Create an Export Fallback with export default
challengeType: 1
---
## Description
In the export lesson, you learned about the syntax referred to as a named export. This allowed you to make multiple functions and variables available for use in other files.
There is another export syntax you need to know, known as export default. Usually you will use this syntax if only one value is being exported from a file. It is also used to create a fallback value for a file or module.
Here is a quick example of export default:
export default function add(x,y) {
return x + y;
}
Note: Since export default is used to declare a fallback value for a module or file, you can only have one value be a default export in each module or file. Additionally, you cannot use export default with var, let, or const
## Instructions
The following function should be the fallback value for the module. Please add the necessary code to do so.
## Tests
```yml
tests:
- text: Proper used of export fallback.
testString: 'getUserInput => assert(getUserInput("index").match(/export\s+default\s+function\s+subtract\(x,y\)\s+{return\s+x\s-\s+y;}/g), "Proper used of export fallback.");'
```
## Challenge Seed
```js
"use strict";
function subtract(x,y) {return x - y;}
```
### Before Test
```js
window.exports = function(){};
```
## Solution
```js
// solution required
```