95 lines
3.4 KiB
Markdown
95 lines
3.4 KiB
Markdown
---
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id: 56533eb9ac21ba0edf2244c9
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title: Accessing Object Properties with Variables
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challengeType: 1
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guideUrl: 'https://www.freecodecamp.org/guide/certificates/accessing-objects-properties-with-variables'
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---
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## Description
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<section id='description'>
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Another use of bracket notation on objects is to access a property which is stored as the value of a variable. This can be very useful for iterating through an object's properties or when accessing a lookup table.
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Here is an example of using a variable to access a property:
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<blockquote>var dogs = {<br> Fido: "Mutt",
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Hunter: "Doberman",
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Snoopie: "Beagle"<br>};<br>var myDog = "Hunter";<br>var myBreed = dogs[myDog];<br>console.log(myBreed); // "Doberman"</blockquote>
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Another way you can use this concept is when the property's name is collected dynamically during the program execution, as follows:
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<blockquote>var someObj = {<br> propName: "John"<br>};<br>function propPrefix(str) {<br> var s = "prop";<br> return s + str;<br>}<br>var someProp = propPrefix("Name"); // someProp now holds the value 'propName'<br>console.log(someObj[someProp]); // "John"</blockquote>
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Note that we do <em>not</em> use quotes around the variable name when using it to access the property because we are using the <em>value</em> of the variable, not the <em>name</em>.
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</section>
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## Instructions
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<section id='instructions'>
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Use the <code>playerNumber</code> variable to look up player <code>16</code> in <code>testObj</code> using bracket notation. Then assign that name to the <code>player</code> variable.
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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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tests:
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- text: <code>playerNumber</code> should be a number
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testString: 'assert(typeof playerNumber === "number", "<code>playerNumber</code> should be a number");'
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- text: The variable <code>player</code> should be a string
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testString: 'assert(typeof player === "string", "The variable <code>player</code> should be a string");'
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- text: The value of <code>player</code> should be "Montana"
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testString: 'assert(player === "Montana", "The value of <code>player</code> should be "Montana"");'
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- text: You should use bracket notation to access <code>testObj</code>
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testString: 'assert(/testObj\s*?\[.*?\]/.test(code),"You should use bracket notation to access <code>testObj</code>");'
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- text: You should not assign the value <code>Montana</code> to the variable <code>player</code> directly.
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testString: 'assert(!code.match(/player\s*=\s*"|\"\s*Montana\s*"|\"\s*;/gi),"You should not assign the value <code>Montana</code> to the variable <code>player</code> directly.");'
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- text: You should be using the variable <code>playerNumber</code> in your bracket notation
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testString: 'assert(/testObj\s*?\[\s*playerNumber\s*\]/.test(code),"You should be using the variable <code>playerNumber</code> in your bracket notation");'
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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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// Setup
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var testObj = {
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12: "Namath",
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16: "Montana",
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19: "Unitas"
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};
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// Only change code below this line;
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var playerNumber; // Change this Line
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var player = testObj; // Change this Line
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```
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</div>
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### After Test
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<div id='js-teardown'>
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```js
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console.info('after the test');
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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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var testObj = {
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12: "Namath",
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16: "Montana",
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19: "Unitas"
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};
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var playerNumber = 16;
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var player = testObj[playerNumber];
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```
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</section>
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