116 lines
2.8 KiB
Markdown
116 lines
2.8 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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Say you want to match a word that occurs multiple times like below.
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```js
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let repeatStr = "row row row your boat";
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```
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You could use `/row row row/`, but what if you don't know the specific word repeated? <dfn>Capture groups</dfn> can be used to find repeated substrings.
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Capture groups are constructed by enclosing the regex pattern to be captured in parentheses. In this case, the goal is to capture a word consisting of alphanumeric characters so the capture group will be `\w+` enclosed by parentheses: `/(\w+)/`.
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The substring matched by the group is saved to a temporary "variable", which can be accessed within the same regex using a backslash and the number of the capture group (e.g. `\1`). Capture groups are automatically numbered by the position of their opening parentheses (left to right), starting at 1.
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The example below matches a word that occurs thrice separated by spaces:
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```js
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let repeatRegex = /(\w+) \1 \1/;
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repeatRegex.test(repeatStr); // Returns true
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repeatStr.match(repeatRegex); // Returns ["row row row", "row"]
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```
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Using the `.match()` method on a string will return an array with the matched substring, along with its captured groups.
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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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reRegex.lastIndex = 0;
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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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reRegex.lastIndex = 0;
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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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reRegex.lastIndex = 0;
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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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reRegex.lastIndex = 0;
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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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reRegex.lastIndex = 0;
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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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