92 lines
2.4 KiB
Markdown
92 lines
2.4 KiB
Markdown
---
|
|
id: 587d7b87367417b2b2512b43
|
|
title: Use Arrow Functions to Write Concise Anonymous Functions
|
|
challengeType: 1
|
|
forumTopicId: 301211
|
|
---
|
|
|
|
## Description
|
|
<section id='description'>
|
|
In JavaScript, we often don't need to name our functions, especially when passing a function as an argument to another function. Instead, we create inline functions. We don't need to name these functions because we do not reuse them anywhere else.
|
|
To achieve this, we often use the following syntax:
|
|
|
|
```js
|
|
const myFunc = function() {
|
|
const myVar = "value";
|
|
return myVar;
|
|
}
|
|
```
|
|
|
|
ES6 provides us with the syntactic sugar to not have to write anonymous functions this way. Instead, you can use <strong>arrow function syntax</strong>:
|
|
|
|
```js
|
|
const myFunc = () => {
|
|
const myVar = "value";
|
|
return myVar;
|
|
}
|
|
```
|
|
|
|
When there is no function body, and only a return value, arrow function syntax allows you to omit the keyword <code>return</code> as well as the brackets surrounding the code. This helps simplify smaller functions into one-line statements:
|
|
|
|
```js
|
|
const myFunc = () => "value";
|
|
```
|
|
|
|
This code will still return <code>value</code> by default.
|
|
</section>
|
|
|
|
## Instructions
|
|
<section id='instructions'>
|
|
Rewrite the function assigned to the variable <code>magic</code> which returns a new <code>Date()</code> to use arrow function syntax. Also make sure nothing is defined using the keyword <code>var</code>.
|
|
</section>
|
|
|
|
## Tests
|
|
<section id='tests'>
|
|
|
|
```yml
|
|
tests:
|
|
- text: User should replace <code>var</code> keyword.
|
|
testString: getUserInput => assert(!getUserInput('index').match(/var/g));
|
|
- text: <code>magic</code> should be a constant variable (by using <code>const</code>).
|
|
testString: getUserInput => assert(getUserInput('index').match(/const\s+magic/g));
|
|
- text: <code>magic</code> should be a <code>function</code>.
|
|
testString: assert(typeof magic === 'function');
|
|
- text: <code>magic()</code> should return correct date.
|
|
testString: assert(magic().setHours(0,0,0,0) === new Date().setHours(0,0,0,0));
|
|
- text: <code>function</code> keyword should not be used.
|
|
testString: getUserInput => assert(!getUserInput('index').match(/function/g));
|
|
|
|
```
|
|
|
|
</section>
|
|
|
|
## Challenge Seed
|
|
<section id='challengeSeed'>
|
|
|
|
<div id='js-seed'>
|
|
|
|
```js
|
|
var magic = function() {
|
|
"use strict";
|
|
return new Date();
|
|
};
|
|
```
|
|
|
|
</div>
|
|
|
|
|
|
|
|
</section>
|
|
|
|
## Solution
|
|
<section id='solution'>
|
|
|
|
```js
|
|
const magic = () => {
|
|
"use strict";
|
|
return new Date();
|
|
};
|
|
```
|
|
|
|
</section>
|