78 lines
3.6 KiB
Markdown
78 lines
3.6 KiB
Markdown
---
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id: 587d7dbb367417b2b2512baa
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title: Reuse Patterns Using Capture Groups
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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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Some patterns you search for will occur multiple times in a string. It is wasteful to manually repeat that regex. There is a better way to specify when you have multiple repeat substrings in your string.
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You can search for repeat substrings using <code>capture groups</code>. Parentheses, <code>(</code> and <code>)</code>, are used to find repeat substrings. You put the regex of the pattern that will repeat in between the parentheses.
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To specify where that repeat string will appear, you use a backslash (<code>\</code>) and then a number. This number starts at 1 and increases with each additional capture group you use. An example would be <code>\1</code> to match the first group.
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The example below matches any word that occurs twice separated by a space:
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<blockquote>let repeatStr = "regex regex";<br>let repeatRegex = /(\w+)\s\1/;<br>repeatRegex.test(repeatStr); // Returns true<br>repeatStr.match(repeatRegex); // Returns ["regex regex", "regex"]</blockquote>
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Using the <code>.match()</code> method on a string will return an array with the string it matches, along with its capture group.
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</section>
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## Instructions
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<section id='instructions'>
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Use <code>capture groups</code> in <code>reRegex</code> to match numbers that are repeated only three times in a string, each separated by a space.
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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 regex should use the shorthand character class for digits.
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testString: assert(reRegex.source.match(/\\d/), 'Your regex should use the shorthand character class for digits.');
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- text: Your regex should reuse the capture group twice.
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testString: assert(reRegex.source.match(/\\\d/g).length === 2, 'Your regex should reuse the capture group twice.');
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- text: Your regex should have two spaces separating the three numbers.
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testString: assert(reRegex.source.match(/\\s/g).length === 2, 'Your regex should have two spaces separating the three numbers.');
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- text: Your regex should match <code>"42 42 42"</code>.
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testString: assert(reRegex.test("42 42 42"), 'Your regex should match <code>"42 42 42"</code>.');
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- text: Your regex should match <code>"100 100 100"</code>.
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testString: assert(reRegex.test("100 100 100"), 'Your regex should match <code>"100 100 100"</code>.');
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- text: Your regex should not match <code>"42 42 42 42"</code>.
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testString: assert.equal(("42 42 42 42").match(reRegex.source), null, 'Your regex should not match <code>"42 42 42 42"</code>.');
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- text: Your regex should not match <code>"42 42"</code>.
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testString: assert.equal(("42 42").match(reRegex.source), null, 'Your regex should not match <code>"42 42"</code>.');
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- text: Your regex should not match <code>"101 102 103"</code>.
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testString: assert(!reRegex.test("101 102 103"), 'Your regex should not match <code>"101 102 103"</code>.');
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- text: Your regex should not match <code>"1 2 3"</code>.
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testString: assert(!reRegex.test("1 2 3"), 'Your regex should not match <code>"1 2 3"</code>.');
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- text: Your regex should match <code>"10 10 10"</code>.
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testString: assert(reRegex.test("10 10 10"), 'Your regex should match <code>"10 10 10"</code>.');
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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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let repeatNum = "42 42 42";
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let reRegex = /change/; // Change this line
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let result = reRegex.test(repeatNum);
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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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let repeatNum = "42 42 42";
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let reRegex = /^(\d+)\s\1\s\1$/;
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let result = reRegex.test(repeatNum);
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```
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</section>
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