bd68b70f3d
* fix: remove isHidden flag from frontmatter * fix: add isUpcomingChange Co-authored-by: Ahmad Abdolsaheb <ahmad.abdolsaheb@gmail.com> * feat: hide blocks not challenges Co-authored-by: Ahmad Abdolsaheb <ahmad.abdolsaheb@gmail.com> Co-authored-by: Ahmad Abdolsaheb <ahmad.abdolsaheb@gmail.com>
115 lines
2.9 KiB
Markdown
115 lines
2.9 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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videoUrl: 'https://scrimba.com/c/cnQyKur'
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forumTopicId: 16165
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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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```js
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var dogs = {
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Fido: "Mutt", Hunter: "Doberman", Snoopie: "Beagle"
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};
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var myDog = "Hunter";
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var myBreed = dogs[myDog];
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console.log(myBreed); // "Doberman"
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```
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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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```js
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var someObj = {
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propName: "John"
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};
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function propPrefix(str) {
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var s = "prop";
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return s + str;
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}
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var someProp = propPrefix("Name"); // someProp now holds the value 'propName'
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console.log(someObj[someProp]); // "John"
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```
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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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Set the <code>playerNumber</code> variable to <code>16</code>. Then, use the variable to look up the player's name and assign it to <code>player</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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tests:
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- text: <code>playerNumber</code> should be a number
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testString: assert(typeof playerNumber === 'number');
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- text: The variable <code>player</code> should be a string
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testString: assert(typeof player === 'string');
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- text: The value of <code>player</code> should be "Montana"
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testString: assert(player === '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));
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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));
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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));
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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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if(typeof player !== "undefined"){(function(v){return v;})(player);}
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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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