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>
82 lines
2.1 KiB
Markdown
82 lines
2.1 KiB
Markdown
---
|
|
id: 56533eb9ac21ba0edf2244aa
|
|
title: Understanding Uninitialized Variables
|
|
challengeType: 1
|
|
videoUrl: 'https://scrimba.com/c/cBa2JAL'
|
|
forumTopicId: 18335
|
|
---
|
|
|
|
## Description
|
|
<section id='description'>
|
|
When JavaScript variables are declared, they have an initial value of <code>undefined</code>. If you do a mathematical operation on an <code>undefined</code> variable your result will be <code>NaN</code> which means <dfn>"Not a Number"</dfn>. If you concatenate a string with an <code>undefined</code> variable, you will get a literal <dfn>string</dfn> of <code>"undefined"</code>.
|
|
</section>
|
|
|
|
## Instructions
|
|
<section id='instructions'>
|
|
Initialize the three variables <code>a</code>, <code>b</code>, and <code>c</code> with <code>5</code>, <code>10</code>, and <code>"I am a"</code> respectively so that they will not be <code>undefined</code>.
|
|
</section>
|
|
|
|
## Tests
|
|
<section id='tests'>
|
|
|
|
```yml
|
|
tests:
|
|
- text: <code>a</code> should be defined and evaluated to have the value of <code>6</code>.
|
|
testString: assert(typeof a === 'number' && a === 6);
|
|
- text: <code>b</code> should be defined and evaluated to have the value of <code>15</code>.
|
|
testString: assert(typeof b === 'number' && b === 15);
|
|
- text: <code>c</code> should not contain <code>undefined</code> and should have a value of "I am a String!"
|
|
testString: assert(!/undefined/.test(c) && c === "I am a String!");
|
|
- text: You should not change code below the specified comment.
|
|
testString: assert(/a = a \+ 1;/.test(code) && /b = b \+ 5;/.test(code) && /c = c \+ " String!";/.test(code));
|
|
|
|
```
|
|
|
|
</section>
|
|
|
|
## Challenge Seed
|
|
<section id='challengeSeed'>
|
|
|
|
<div id='js-seed'>
|
|
|
|
```js
|
|
// Only change code below this line
|
|
var a;
|
|
var b;
|
|
var c;
|
|
// Only change code above this line
|
|
|
|
a = a + 1;
|
|
b = b + 5;
|
|
c = c + " String!";
|
|
```
|
|
|
|
</div>
|
|
|
|
|
|
### After Test
|
|
<div id='js-teardown'>
|
|
|
|
```js
|
|
(function(a,b,c){ return "a = " + a + ", b = " + b + ", c = '" + c + "'"; })(a,b,c);
|
|
```
|
|
|
|
</div>
|
|
|
|
</section>
|
|
|
|
## Solution
|
|
<section id='solution'>
|
|
|
|
|
|
```js
|
|
var a = 5;
|
|
var b = 10;
|
|
var c = "I am a";
|
|
a = a + 1;
|
|
b = b + 5;
|
|
c = c + " String!";
|
|
```
|
|
|
|
</section>
|