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) |
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 |
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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