84 lines
2.7 KiB
Markdown
84 lines
2.7 KiB
Markdown
---
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id: 587d78b2367417b2b2512b0e
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title: Add Items to an Array with push() and unshift()
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challengeType: 1
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forumTopicId: 301151
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---
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## Description
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<section id='description'>
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An array's length, like the data types it can contain, is not fixed. Arrays can be defined with a length of any number of elements, and elements can be added or removed over time; in other words, arrays are <dfn>mutable</dfn>. In this challenge, we will look at two methods with which we can programmatically modify an array: <code>Array.push()</code> and <code>Array.unshift()</code>.
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Both methods take one or more elements as parameters and add those elements to the array the method is being called on; the <code>push()</code> method adds elements to the end of an array, and <code>unshift()</code> adds elements to the beginning. Consider the following:
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```js
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let twentyThree = 'XXIII';
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let romanNumerals = ['XXI', 'XXII'];
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romanNumerals.unshift('XIX', 'XX');
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// now equals ['XIX', 'XX', 'XXI', 'XXII']
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romanNumerals.push(twentyThree);
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// now equals ['XIX', 'XX', 'XXI', 'XXII', 'XXIII']Notice that we can also pass variables, which allows us even greater flexibility in dynamically modifying our array's data.
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```
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</section>
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## Instructions
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<section id='instructions'>
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We have defined a function, <code>mixedNumbers</code>, which we are passing an array as an argument. Modify the function by using <code>push()</code> and <code>unshift()</code> to add <code>'I', 2, 'three'</code> to the beginning of the array and <code>7, 'VIII', 9</code> to the end so that the returned array contains representations of the numbers 1-9 in order.
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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>mixedNumbers(["IV", 5, "six"])</code> should now return <code>["I", 2, "three", "IV", 5, "six", 7, "VIII", 9]</code>
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testString: assert.deepEqual(mixedNumbers(['IV', 5, 'six']), ['I', 2, 'three', 'IV', 5, 'six', 7, 'VIII', 9]);
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- text: The <code>mixedNumbers</code> function should utilize the <code>push()</code> method
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testString: assert(mixedNumbers.toString().match(/\.push/));
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- text: The <code>mixedNumbers</code> function should utilize the <code>unshift()</code> method
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testString: assert(mixedNumbers.toString().match(/\.unshift/));
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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 mixedNumbers(arr) {
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// change code below this line
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// change code above this line
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return arr;
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}
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// do not change code below this line
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console.log(mixedNumbers(['IV', 5, 'six']));
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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 mixedNumbers(arr) {
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// change code below this line
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arr.push(7,'VIII',9);
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arr.unshift('I',2,'three');
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// change code above this line
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return arr;
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}
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```
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</section>
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