121 lines
3.3 KiB
Markdown
121 lines
3.3 KiB
Markdown
---
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title: 6 JavaScript Regular Expression features you can use today
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shortTitle: JavaScript Regular Expression tips
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type: story
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tags: [javascript,string,regexp]
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author: chalarangelo
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cover: taking-photos
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excerpt: Regular expressions are very powerful, but hard to master. Understand these features and start using them in your JavaScript code.
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dateModified: 2021-06-12T19:30:41+03:00
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---
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Regular expressions, while very powerful, are notoriously hard to master. Here are 6 useful features that can help you start using them in your JavaScript projects:
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### Capturing groups
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Capturing groups allow you to get specific parts of the matched string, simply by wrapping part of the regular expression in parentheses `(...)`:
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```js
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const str = 'JavaScript is a programming language';
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/(JavaScript) is a (.*)/.exec(str);
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/*
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[
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0: 'JavaScript is a programming language',
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1: 'JavaScript',
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2: 'programming language'
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]
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*/
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```
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### Non-capturing groups
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Non-capturing groups are used for matching something without capturing it, like an either/or matching group that you do not really need. They are defined similarly to capturing groups, but prefixed with `?:`:
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```js
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const str = 'JavaScript is a programming language';
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/(?:JavaScript|Python) is a (.+)/.exec(str);
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/*
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[
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0: 'JavaScript is a programming language',
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1: 'programming language'
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]
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*/
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```
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### Named capturing groups
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Named capturing groups allow you to name a capturing group, by prefixing it with `<name>`:
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```js
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const str = 'JavaScript is a programming language';
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/(?<subject>.+) is a (?<description>.+)/.exec(str);
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/*
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[
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0: 'JavaScript is a programming language',
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1: 'JavaScript',
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2: 'programming language',
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groups: {
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subject: 'JavaScript,
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description: 'programming language'
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}
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]
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*/
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```
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### Capturing group backreferences
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Backreferences help you write shorter regular expressions, by repeating an existing capturing group, using `\1`, `\2` etc. Similarly, you can also repeat named capturing groups using `\k<name>`:
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```js
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const str = 'JavaScript is a programming language - an awesome programming language JavaScript is';
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/(.+) is a (?<description>.+) - an awesome \k<description> \1 is/.exec(str);
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/*
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[
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0: 'JavaScript is a programming language - an awesome programming language JavaScript is',
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1: 'JavaScript',
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2: 'programming language',
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groups: {
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subject: 'JavaScript,
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description: 'programming language'
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}
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]
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*/
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```
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### Lookaheads
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Lookaheads allow you to check if something is followed by a certain pattern, without actually matching it. You can create positive lookaheads using `?=` and negative lookaheads using `?!`:
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```js
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const str = 'JavaScript is not the same as Java and you should remember that';
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/Java(?=Script)(.*)/.exec(str);
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/*
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[
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0: 'JavaScript is not the same as Java and you should remember that',
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1: 'Script is not the same as Java and you should remember that'
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]
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*/
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/Java(?!Script)(.*)/.exec(str);
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/*
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[
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0: 'Java and you should remember that',
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1: ' and you should remember that'
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]
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*/
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```
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### Unicode characters
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Finally, you can match unicode characters, using `/p{...}` and the `/u` flag. Examples include, but are not limited to `{Emoji}`, `{Math_Symbols}` and `{Script=Greek}`:
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```js
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const str = 'Greek looks like this: γεια';
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/\p{Script=Greek}+/u.exec(str);
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/*
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[
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0: 'γεια'
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]
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*/
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```
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