74 lines
2.8 KiB
Markdown
74 lines
2.8 KiB
Markdown
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---
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id: 587d7daf367417b2b2512b7e
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title: Understand the Constructor Property
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challengeType: 1
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---
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## Description
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<section id='description'>
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There is a special <code>constructor</code> property located on the object instances <code>duck</code> and <code>beagle</code> that were created in the previous challenges:
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<blockquote>let duck = new Bird();<br>let beagle = new Dog();<br><br>console.log(duck.constructor === Bird); //prints true<br>console.log(beagle.constructor === Dog); //prints true</blockquote>
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Note that the <code>constructor</code> property is a reference to the constructor function that created the instance.
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The advantage of the <code>constructor</code> property is that it's possible to check for this property to find out what kind of object it is. Here's an example of how this could be used:
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<blockquote>function joinBirdFraternity(candidate) {<br> if (candidate.constructor === Bird) {<br> return true;<br> } else {<br> return false;<br> }<br>}</blockquote>
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<strong>Note</strong><br>Since the <code>constructor</code> property can be overwritten (which will be covered in the next two challenges) it’s generally better to use the <code>instanceof</code> method to check the type of an object.
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</section>
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## Instructions
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<section id='instructions'>
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Write a <code>joinDogFraternity</code> function that takes a <code>candidate</code> parameter and, using the <code>constructor</code> property, return <code>true</code> if the candidate is a <code>Dog</code>, otherwise return <code>false</code>.
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</section>
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## Tests
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<section id='tests'>
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```yml
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- text: <code>joinDogFraternity</code> should be defined as a function.
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testString: 'assert(typeof(joinDogFraternity) === "function", "<code>joinDogFraternity</code> should be defined as a function.");'
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- text: <code>joinDogFraternity</code> should return true if<code>candidate</code> is an instance of <code>Dog</code>.
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testString: 'assert(joinDogFraternity(new Dog("")) === true, "<code>joinDogFraternity</code> should return true if<code>candidate</code> is an instance of <code>Dog</code>.");'
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- text: <code>joinDogFraternity</code> should use the <code>constructor</code> property.
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testString: 'assert(/\.constructor/.test(code) && !/instanceof/.test(code), "<code>joinDogFraternity</code> should use the <code>constructor</code> property.");'
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='js-seed'>
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```js
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function Dog(name) {
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this.name = name;
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}
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// Add your code below this line
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function joinDogFraternity(candidate) {
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}
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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function Dog(name) {
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this.name = name;
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}
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function joinDogFraternity(candidate) {
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return candidate.constructor === Dog;
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}
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```
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</section>
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