f1c9b08cf3
This includes certificates (where it does nothing), but does not include any translations.
85 lines
2.4 KiB
Markdown
85 lines
2.4 KiB
Markdown
---
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id: 587d7da9367417b2b2512b67
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title: Add Elements to the End of an Array Using concat Instead of push
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challengeType: 1
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isHidden: false
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forumTopicId: 301226
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---
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## Description
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<section id='description'>
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Functional programming is all about creating and using non-mutating functions.
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The last challenge introduced the <code>concat</code> method as a way to combine arrays into a new one without mutating the original arrays. Compare <code>concat</code> to the <code>push</code> method. <code>Push</code> adds an item to the end of the same array it is called on, which mutates that array. Here's an example:
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```js
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var arr = [1, 2, 3];
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arr.push([4, 5, 6]);
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// arr is changed to [1, 2, 3, [4, 5, 6]]
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// Not the functional programming way
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```
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<code>Concat</code> offers a way to add new items to the end of an array without any mutating side effects.
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</section>
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## Instructions
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<section id='instructions'>
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Change the <code>nonMutatingPush</code> function so it uses <code>concat</code> to add <code>newItem</code> to the end of <code>original</code> instead of <code>push</code>. The function should return an array.
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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: Your code should use the <code>concat</code> method.
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testString: assert(code.match(/\.concat/g));
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- text: Your code should not use the <code>push</code> method.
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testString: assert(!code.match(/\.?[\s\S]*?push/g));
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- text: The <code>first</code> array should not change.
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testString: assert(JSON.stringify(first) === JSON.stringify([1, 2, 3]));
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- text: The <code>second</code> array should not change.
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testString: assert(JSON.stringify(second) === JSON.stringify([4, 5]));
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- text: <code>nonMutatingPush([1, 2, 3], [4, 5])</code> should return <code>[1, 2, 3, 4, 5]</code>.
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testString: assert(JSON.stringify(nonMutatingPush([1, 2, 3], [4, 5])) === JSON.stringify([1, 2, 3, 4, 5]));
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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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function nonMutatingPush(original, newItem) {
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// Only change code below this line
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return original.push(newItem);
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// Only change code above this line
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}
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var first = [1, 2, 3];
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var second = [4, 5];
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nonMutatingPush(first, second);
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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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function nonMutatingPush(original, newItem) {
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return original.concat(newItem);
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}
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var first = [1, 2, 3];
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var second = [4, 5];
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nonMutatingPush(first, second);
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```
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</section>
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