JavaScript Regular Expression Cheat Sheet

A list of regex expressions for quick access

Ferenc Almasi • 2022 April 28 •

1 min read

Regular expressions can be hard to remember, no wonder you have landed on this page. Below you will find a full list of regular expressions you can use in JavaScript with their meaning explained.

Flags

Flag	Explanation
`g`	Match globally
`i`	Case insensitive matching
`m`	Match on multiple lines when using anchors
`s` (dotall)	Makes `.` to match new lines as well
`u`	Unicode support

Anchors

Regex	Explanation
`^a`	Starts with the next character (a)
`z$`	Ends with the preceding character (z)

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Character Classes

Regex	Explanation
`\w`	Match for word
`\d`	Match for digit
`\s`	Match for whitespace
`\W`	Match any character that is not a word
`\D`	Match any character that is not a digit
`\S`	Match any character that is not a whitespace
`[az]`	Match any of "a" and "z"
`[^az]`	Match any character that is not "a" and "z"
`[a-z]`	Match a set of characters inside the brackets (a to z)
`.`	Match everything expect a new line

Quantifiers and Alternations

Regex	Explanation
`a{4}`	Match preceding token that is exactly 4 characters long
`a{2,4}`	Match preceding token that is between 2 and 4 characters long
`a{2,}`	Match preceding token longer than 2 characters
`a*`	Match 0 or more of the preceding character
`a+`	Match 1 or more of the preceding character
`a?`	Match 0 or 1 of the preceding character
`a\|z`	Match “a” or “z”

Escaped Characters

Regex	Explanation
`\/`	Escape a forward slash (char code 47)
`\\`	Escape a backslash (char code 92)
`\.`	Escape a dot (char code 46)
`\*`	Escape an asterisk
`\t`	Match tabs
`\n`	Match new line
`\r`	Match carriage return

Groups and Lookarounds

Regex	Explanation
`(2020)`	Capturing group - group the expression when there is a match
`(?:2020)`	Non-capturing group - don't capture the expression
`(?<year>2020)`	Named capturing group - name the captured group as "year"
`(?=2020)`	Positive lookahead - see if pattern is followed by the expression
`(?!2020)`	Negative lookahead - see if pattern is not followed by the expression
`(?<=2020)`	Positive lookbehind - see if pattern is preceded by the expression
`(?<!2020)`	Negative lookbehind - see if pattern is not preceded by the expression

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JavaScript Functions

Function	Return value
`regex.exec('string')`	Returns `null` or `array` containing the match
`regex.test('string')`	Returns `true` or `false` based on the provided string
`string.match(/regex/g)`	Returns `null` or `array` containing matches
`string.matchAll(/regex/g)`	Returns an empty array or `RegExpStringIterator`
`string.search(/regex/g)`	Returns index, returns `-1` if no match is found
`string.replace(/regex/g, 'newString')`	Returns a string where the matched expression is replaced with the second argument
`string.replaceAll(/regex/g, 'newString')`	Returns a string where all occurrences of the matched expression are replaced with the second argument
`string.split(/regex/g)`	Breaks the string into an array of substrings based on the expression

Tools

Site	Description
regexr.com	Test your regular expressions interactively
regexper.com	Visualize your regular expressions

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