107 lines
2.6 KiB
Markdown
107 lines
2.6 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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forumTopicId: 301364
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dashedName: reuse-patterns-using-capture-groups
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---
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# --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 <dfn>capture groups</dfn>. Parentheses, `(` and `)`, 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 (`\`) and then a number. This number starts at 1 and increases with each additional capture group you use. An example would be `\1` 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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```js
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let repeatStr = "regex regex";
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let repeatRegex = /(\w+)\s\1/;
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repeatRegex.test(repeatStr);
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repeatStr.match(repeatRegex);
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```
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The `test` call would return `true`, and the `match` call would return `["regex regex", "regex"]`.
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Using the `.match()` method on a string will return an array with the string it matches, along with its capture group.
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# --instructions--
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Use capture groups in `reRegex` to match a string that consists of only the same number repeated exactly three times separated by single spaces.
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# --hints--
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Your regex should use the shorthand character class for digits.
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```js
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assert(reRegex.source.match(/\\d/));
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```
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Your regex should reuse a capture group twice.
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```js
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assert(reRegex.source.match(/\\1|\\2/g).length >= 2);
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```
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Your regex should match the string `42 42 42`.
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```js
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assert(reRegex.test('42 42 42'));
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```
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Your regex should match the string `100 100 100`.
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```js
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assert(reRegex.test('100 100 100'));
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```
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Your regex should not match the string `42 42 42 42`.
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```js
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assert.equal('42 42 42 42'.match(reRegex.source), null);
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```
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Your regex should not match the string `42 42`.
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```js
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assert.equal('42 42'.match(reRegex.source), null);
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```
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Your regex should not match the string `101 102 103`.
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```js
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assert(!reRegex.test('101 102 103'));
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```
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Your regex should not match the string `1 2 3`.
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```js
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assert(!reRegex.test('1 2 3'));
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```
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Your regex should match the string `10 10 10`.
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```js
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assert(reRegex.test('10 10 10'));
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```
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# --seed--
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## --seed-contents--
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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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# --solutions--
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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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