71 lines
2.5 KiB
Markdown
71 lines
2.5 KiB
Markdown
|
---
|
||
|
|
id: 587d7dae367417b2b2512b7a
|
||
|
|
title: Verify an Object's Constructor with instanceof
|
||
|
|
challengeType: 1
|
||
|
|
---
|
||
|
|
|
||
|
|
## Description
|
||
|
|
<section id='description'>
|
||
|
|
Anytime a constructor function creates a new object, that object is said to be an <code>instance</code> of its constructor. JavaScript gives a convenient way to verify this with the <code>instanceof</code> operator. <code>instanceof</code> allows you to compare an object to a constructor, returning <code>true</code> or <code>false</code> based on whether or not that object was created with the constructor. Here's an example:
|
||
|
|
<blockquote>let Bird = function(name, color) {<br> this.name = name;<br> this.color = color;<br> this.numLegs = 2;<br>}<br><br>let crow = new Bird("Alexis", "black");<br><br>crow instanceof Bird; // => true</blockquote>
|
||
|
|
If an object is created without using a constructor, <code>instanceof</code> will verify that it is not an instance of that constructor:
|
||
|
|
<blockquote>let canary = {<br> name: "Mildred",<br> color: "Yellow",<br> numLegs: 2<br>};<br><br>canary instanceof Bird; // => false</blockquote>
|
||
|
|
</section>
|
||
|
|
|
||
|
|
## Instructions
|
||
|
|
<section id='instructions'>
|
||
|
|
Create a new instance of the <code>House</code> constructor, calling it <code>myHouse</code> and passing a number of bedrooms. Then, use <code>instanceof</code> to verify that it is an instance of <code>House</code>.
|
||
|
|
</section>
|
||
|
|
|
||
|
|
## Tests
|
||
|
|
<section id='tests'>
|
||
|
|
|
||
|
|
```yml
|
||
|
|
tests:
|
||
|
|
- text: <code>myHouse</code> should have a <code>numBedrooms</code> attribute set to a number.
|
||
|
|
testString: 'assert(typeof myHouse.numBedrooms === ''number'', ''<code>myHouse</code> should have a <code>numBedrooms</code> attribute set to a number.'');'
|
||
|
|
- text: Be sure to verify that <code>myHouse</code> is an instance of <code>House</code> using the <code>instanceof</code> operator.
|
||
|
|
testString: 'assert(/myHouse\s*instanceof\s*House/.test(code), ''Be sure to verify that <code>myHouse</code> is an instance of <code>House</code> using the <code>instanceof</code> operator.'');'
|
||
|
|
|
||
|
|
```
|
||
|
|
|
||
|
|
</section>
|
||
|
|
|
||
|
|
## Challenge Seed
|
||
|
|
<section id='challengeSeed'>
|
||
|
|
|
||
|
|
<div id='js-seed'>
|
||
|
|
|
||
|
|
```js
|
||
|
|
/* jshint expr: true */
|
||
|
|
|
||
|
|
function House(numBedrooms) {
|
||
|
|
this.numBedrooms = numBedrooms;
|
||
|
|
}
|
||
|
|
|
||
|
|
// Add your code below this line
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
```
|
||
|
|
|
||
|
|
</div>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
</section>
|
||
|
|
|
||
|
|
## Solution
|
||
|
|
<section id='solution'>
|
||
|
|
|
||
|
|
|
||
|
|
```js
|
||
|
|
function House(numBedrooms) {
|
||
|
|
this.numBedrooms = numBedrooms;
|
||
|
|
}
|
||
|
|
const myHouse = new House(4);
|
||
|
|
console.log(myHouse instanceof House);
|
||
|
|
```
|
||
|
|
|
||
|
|
</section>
|