68 lines
2.5 KiB
Markdown
68 lines
2.5 KiB
Markdown
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---
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id: 587d7b88367417b2b2512b47
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title: Use the Rest Operator with Function Parameters
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challengeType: 1
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---
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## Description
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<section id='description'>
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In order to help us create more flexible functions, ES6 introduces the <dfn>rest operator</dfn> for function parameters. With the rest operator, you can create functions that take a variable number of arguments. These arguments are stored in an array that can be accessed later from inside the function.
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Check out this code:
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<blockquote>function howMany(...args) {<br> return "You have passed " + args.length + " arguments.";<br>}<br>console.log(howMany(0, 1, 2)); // You have passed 3 arguments<br>console.log(howMany("string", null, [1, 2, 3], { })); // You have passed 4 arguments.</blockquote>
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The rest operator eliminates the need to check the <code>args</code> array and allows us to apply <code>map()</code>, <code>filter()</code> and <code>reduce()</code> on the parameters array.
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</section>
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## Instructions
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<section id='instructions'>
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Modify the function <code>sum</code> so that it uses the rest operator and it works in the same way with any number of parameters.
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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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- text: 'The result of <code>sum(0,1,2)</code> should be 3'
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testString: 'assert(sum(0,1,2) === 3, "The result of <code>sum(0,1,2)</code> should be 3");'
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- text: 'The result of <code>sum(1,2,3,4)</code> should be 10'
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testString: 'assert(sum(1,2,3,4) === 10, "The result of <code>sum(1,2,3,4)</code> should be 10");'
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- text: The result of <code>sum(5)</code> should be 5
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testString: 'assert(sum(5) === 5, "The result of <code>sum(5)</code> should be 5");'
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- text: The result of <code>sum()</code> should be 0
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testString: 'assert(sum() === 0, "The result of <code>sum()</code> should be 0");'
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- text: The <code>sum</code> function uses the <code>...</code> spread operator on the <code>args</code> parameter.
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testString: 'getUserInput => assert(getUserInput("index").match(/function\s+sum\s*\(\s*...args\s*\)\s*{/g), "The <code>sum</code> function uses the <code>...</code> spread operator on the <code>args</code> parameter.");'
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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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const sum = (function() {
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"use strict";
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return function sum(x, y, z) {
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const args = [ x, y, z ];
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return args.reduce((a, b) => a + b, 0);
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};
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})();
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console.log(sum(1, 2, 3)); // 6
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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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// solution required
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```
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</section>
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