83 lines
2.3 KiB
Markdown
83 lines
2.3 KiB
Markdown
---
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id: 56533eb9ac21ba0edf2244aa
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title: Understanding Uninitialized Variables
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challengeType: 1
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videoUrl: 'https://scrimba.com/c/cBa2JAL'
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---
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## Description
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<section id='description'>
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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>.
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</section>
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## Instructions
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<section id='instructions'>
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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>.
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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>a</code> should be defined and evaluated to have the value of <code>6</code>
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testString: assert(typeof a === 'number' && a === 6, '<code>a</code> should be defined and evaluated to have the value of <code>6</code>');
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- text: <code>b</code> should be defined and evaluated to have the value of <code>15</code>
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testString: assert(typeof b === 'number' && b === 15, '<code>b</code> should be defined and evaluated to have the value of <code>15</code>');
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- text: <code>c</code> should not contain <code>undefined</code> and should have a value of "I am a String!"
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testString: assert(!/undefined/.test(c) && c === "I am a String!", '<code>c</code> should not contain <code>undefined</code> and should have a value of "I am a String!"');
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- text: Do not change code below the line
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testString: assert(/a = a \+ 1;/.test(code) && /b = b \+ 5;/.test(code) && /c = c \+ " String!";/.test(code), 'Do not change code below the line');
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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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// Initialize these three variables
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var a;
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var b;
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var c;
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// Do not change code below this line
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a = a + 1;
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b = b + 5;
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c = c + " String!";
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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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(function(a,b,c){ return "a = " + a + ", b = " + b + ", c = '" + c + "'"; })(a,b,c);
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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 a = 5;
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var b = 10;
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var c = "I am a";
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a = a + 1;
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b = b + 5;
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c = c + " String!";
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```
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</section>
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