79d9012432
* fix(curriculum): tests quotes * fix(curriculum): fill seed-teardown * fix(curriculum): fix tests and remove unneeded seed-teardown
95 lines
3.4 KiB
Markdown
95 lines
3.4 KiB
Markdown
---
|
|
id: 56533eb9ac21ba0edf2244c9
|
|
title: Accessing Object Properties with Variables
|
|
challengeType: 1
|
|
guideUrl: 'https://www.freecodecamp.org/guide/certificates/accessing-objects-properties-with-variables'
|
|
---
|
|
|
|
## Description
|
|
<section id='description'>
|
|
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.
|
|
Here is an example of using a variable to access a property:
|
|
<blockquote>var dogs = {<br> Fido: "Mutt",
|
|
Hunter: "Doberman",
|
|
Snoopie: "Beagle"<br>};<br>var myDog = "Hunter";<br>var myBreed = dogs[myDog];<br>console.log(myBreed); // "Doberman"</blockquote>
|
|
Another way you can use this concept is when the property's name is collected dynamically during the program execution, as follows:
|
|
<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>
|
|
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>.
|
|
</section>
|
|
|
|
## Instructions
|
|
<section id='instructions'>
|
|
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.
|
|
</section>
|
|
|
|
## Tests
|
|
<section id='tests'>
|
|
|
|
```yml
|
|
tests:
|
|
- text: <code>playerNumber</code> should be a number
|
|
testString: assert(typeof playerNumber === 'number', '<code>playerNumber</code> should be a number');
|
|
- text: The variable <code>player</code> should be a string
|
|
testString: assert(typeof player === 'string', 'The variable <code>player</code> should be a string');
|
|
- text: The value of <code>player</code> should be "Montana"
|
|
testString: assert(player === 'Montana', 'The value of <code>player</code> should be "Montana"');
|
|
- text: You should use bracket notation to access <code>testObj</code>
|
|
testString: assert(/testObj\s*?\[.*?\]/.test(code),'You should use bracket notation to access <code>testObj</code>');
|
|
- text: You should not assign the value <code>Montana</code> to the variable <code>player</code> directly.
|
|
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.');
|
|
- text: You should be using the variable <code>playerNumber</code> in your bracket notation
|
|
testString: assert(/testObj\s*?\[\s*playerNumber\s*\]/.test(code),'You should be using the variable <code>playerNumber</code> in your bracket notation');
|
|
|
|
```
|
|
|
|
</section>
|
|
|
|
## Challenge Seed
|
|
<section id='challengeSeed'>
|
|
|
|
<div id='js-seed'>
|
|
|
|
```js
|
|
// Setup
|
|
var testObj = {
|
|
12: "Namath",
|
|
16: "Montana",
|
|
19: "Unitas"
|
|
};
|
|
|
|
// Only change code below this line;
|
|
|
|
var playerNumber; // Change this Line
|
|
var player = testObj; // Change this Line
|
|
```
|
|
|
|
</div>
|
|
|
|
|
|
### After Test
|
|
<div id='js-teardown'>
|
|
|
|
```js
|
|
if(typeof player !== "undefined"){(function(v){return v;})(player);}
|
|
```
|
|
|
|
</div>
|
|
|
|
</section>
|
|
|
|
## Solution
|
|
<section id='solution'>
|
|
|
|
|
|
```js
|
|
var testObj = {
|
|
12: "Namath",
|
|
16: "Montana",
|
|
19: "Unitas"
|
|
};
|
|
var playerNumber = 16;
|
|
var player = testObj[playerNumber];
|
|
```
|
|
|
|
</section>
|