85 lines
2.4 KiB
Markdown
85 lines
2.4 KiB
Markdown
---
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id: 587d7b8a367417b2b2512b4c
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title: Use Destructuring Assignment with the Rest Parameter to Reassign Array Elements
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challengeType: 1
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forumTopicId: 301218
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---
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## Description
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<section id='description'>
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In some situations involving array destructuring, we might want to collect the rest of the elements into a separate array.
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The result is similar to <code>Array.prototype.slice()</code>, as shown below:
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```js
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const [a, b, ...arr] = [1, 2, 3, 4, 5, 7];
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console.log(a, b); // 1, 2
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console.log(arr); // [3, 4, 5, 7]
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```
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Variables <code>a</code> and <code>b</code> take the first and second values from the array. After that, because of rest parameter's presence, <code>arr</code> gets rest of the values in the form of an array.
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The rest element only works correctly as the last variable in the list. As in, you cannot use the rest parameter to catch a subarray that leaves out last element of the original array.
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</section>
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## Instructions
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<section id='instructions'>
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Use destructuring assignment with the rest parameter to perform an effective <code>Array.prototype.slice()</code> so that <code>arr</code> is a sub-array of the original array <code>source</code> with the first two elements omitted.
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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>arr</code> should be <code>[3,4,5,6,7,8,9,10]</code>
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testString: assert(arr.every((v, i) => v === i + 3) && arr.length === 8);
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- text: <code>Array.slice()</code> should not be used.
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testString: getUserInput => assert(!getUserInput('index').match(/slice/g));
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- text: Destructuring on <code>list</code> should be used.
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testString: assert(code.replace(/\s/g, '').match(/\[(([_$a-z]\w*)?,){1,}\.\.\.arr\]=list/i));
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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 source = [1,2,3,4,5,6,7,8,9,10];
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function removeFirstTwo(list) {
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"use strict";
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// change code below this line
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const arr = list; // change this
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// change code above this line
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return arr;
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}
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const arr = removeFirstTwo(source);
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console.log(arr); // should be [3,4,5,6,7,8,9,10]
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console.log(source); // should be [1,2,3,4,5,6,7,8,9,10];
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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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const source = [1,2,3,4,5,6,7,8,9,10];
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function removeFirstTwo(list) {
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"use strict";
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// change code below this line
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const [, , ...arr] = list;
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// change code above this line
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return arr;
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}
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const arr = removeFirstTwo(source);
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```
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</section>
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