80 lines
3.1 KiB
Markdown
80 lines
3.1 KiB
Markdown
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---
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id: 587d7b7d367417b2b2512b1c
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title: Check if an Object has a 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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Now we can add, modify, and remove keys from objects. But what if we just wanted to know if an object has a specific property? JavaScript provides us with two different ways to do this. One uses the <code>hasOwnProperty()</code> method and the other uses the <code>in</code> keyword. If we have an object <code>users</code> with a property of <code>Alan</code>, we could check for its presence in either of the following ways:
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<blockquote>users.hasOwnProperty('Alan');<br>'Alan' in users;<br>// both return true</blockquote>
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</section>
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## Instructions
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<section id='instructions'>
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We've created an object, <code>users</code>, with some users in it and a function <code>isEveryoneHere</code>, which we pass the <code>users</code> object to as an argument. Finish writing this function so that it returns <code>true</code> only if the <code>users</code> object contains all four names, <code>Alan</code>, <code>Jeff</code>, <code>Sarah</code>, and <code>Ryan</code>, as keys, and <code>false</code> otherwise.
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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: 'The <code>users</code> object only contains the keys <code>Alan</code>, <code>Jeff</code>, <code>Sarah</code>, and <code>Ryan</code>'
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testString: 'assert("Alan" in users && "Jeff" in users && "Sarah" in users && "Ryan" in users && Object.keys(users).length === 4, "The <code>users</code> object only contains the keys <code>Alan</code>, <code>Jeff</code>, <code>Sarah</code>, and <code>Ryan</code>");'
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- text: 'The function <code>isEveryoneHere</code> returns <code>true</code> if <code>Alan</code>, <code>Jeff</code>, <code>Sarah</code>, and <code>Ryan</code> are properties on the <code>users</code> object'
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testString: 'assert(isEveryoneHere(users) === true, "The function <code>isEveryoneHere</code> returns <code>true</code> if <code>Alan</code>, <code>Jeff</code>, <code>Sarah</code>, and <code>Ryan</code> are properties on the <code>users</code> object");'
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- text: 'The function <code>isEveryoneHere</code> returns <code>false</code> if <code>Alan</code>, <code>Jeff</code>, <code>Sarah</code>, and <code>Ryan</code> are not properties on the <code>users</code> object'
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testString: 'assert((function() { delete users.Alan; delete users.Jeff; delete users.Sarah; delete users.Ryan; return isEveryoneHere(users) })() === false, "The function <code>isEveryoneHere</code> returns <code>false</code> if <code>Alan</code>, <code>Jeff</code>, <code>Sarah</code>, and <code>Ryan</code> are not properties on the <code>users</code> object");'
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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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let users = {
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Alan: {
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age: 27,
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online: true
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},
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Jeff: {
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age: 32,
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online: true
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},
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Sarah: {
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age: 48,
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online: true
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},
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Ryan: {
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age: 19,
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online: true
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}
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};
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function isEveryoneHere(obj) {
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// change code below this line
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// change code above this line
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}
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console.log(isEveryoneHere(users));
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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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// solution required
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```
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</section>
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