freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-an.../es6/use-class-syntax-to-define-...

77 lines
2.9 KiB
Markdown
Raw Normal View History

---
id: 587d7b8b367417b2b2512b53
title: Use class Syntax to Define a Constructor Function
challengeType: 1
---
## Description
<section id='description'>
ES6 provides a new syntax to help create objects, using the keyword <dfn>class</dfn>.
This is to be noted, that the <code>class</code> syntax is just a syntax, and not a full-fledged class based implementation of object oriented paradigm, unlike in languages like Java, or Python, or Ruby etc.
In ES5, we usually define a constructor function, and use the <code>new</code> keyword to instantiate an object.
<blockquote>var SpaceShuttle = function(targetPlanet){<br>&nbsp;&nbsp;this.targetPlanet = targetPlanet;<br>}<br>var zeus = new SpaceShuttle('Jupiter');</blockquote>
The class syntax simply replaces the constructor function creation:
<blockquote>class SpaceShuttle {<br>&nbsp;&nbsp;constructor(targetPlanet) {<br>&nbsp;&nbsp;&nbsp;&nbsp;this.targetPlanet = targetPlanet;<br>&nbsp;&nbsp;}<br>}<br>const zeus = new SpaceShuttle('Jupiter');</blockquote>
Notice that the <code>class</code> keyword declares a new function, and a constructor was added, which would be invoked when <code>new</code> is called - to create a new object.<br>
<strong>Notes:</strong><br><ul>
<li> UpperCamelCase should be used by convention for ES6 class names, as in <code>SpaceShuttle</code> used above.</li>
<li> The constructor method is a special method for creating and initializing an object created with a class. You will learn more about it in the Object Oriented Programming section of the JavaScript Algorithms And Data Structures Certification.</li></ul>
</section>
## Instructions
<section id='instructions'>
Use <code>class</code> keyword and write a proper constructor to create the <code>Vegetable</code> class.
The <code>Vegetable</code> lets you create a vegetable object, with a property <code>name</code>, to be passed to constructor.
</section>
## Tests
<section id='tests'>
```yml
tests:
- text: <code>Vegetable</code> should be a <code>class</code> with a defined <code>constructor</code> method.
testString: assert(typeof Vegetable === 'function' && typeof Vegetable.constructor === 'function');
- text: <code>class</code> keyword should be used.
testString: assert(code.match(/class/g));
- text: <code>Vegetable</code> should be able to be instantiated.
testString: assert(() => {const a = new Vegetable("apple"); return typeof a === 'object';});
- text: <code>carrot.name</code> should return <code>carrot</code>.
testString: assert(carrot.name=='carrot');
```
</section>
## Challenge Seed
<section id='challengeSeed'>
<div id='js-seed'>
```js
/* Alter code below this line */
/* Alter code above this line */
const carrot = new Vegetable('carrot');
console.log(carrot.name); // => should be 'carrot'
```
</div>
</section>
## Solution
<section id='solution'>
```js
class Vegetable {
constructor(name) {
this.name = name;
2019-01-24 20:36:57 +00:00
}
}
const carrot = new Vegetable('carrot');
```
</section>