JavaScript/Regular Expressions

Regular Expressions

JavaScript implements regular expressions (regex for short) when searching for matches within a string. As with other scripting languages, this allows searching beyond a simple letter-by-letter match, and can even be used to parse strings in a certain format.

Unlike strings, regular expressions are delimited by the slash (/) character, and may have some options appended.

Regular expressions most commonly appear in conjunction with the string.match() and string.replace() methods.

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Compatibility

JavaScript's set of regular expressions follows the extended set. While copying a Regex pattern from JavaScript to another location may work as expected, some older programs may not function as expected.

In the search term, \1 is used to back reference a matched group, as in other implementations.
In the replacement string, $1 is substituted with a matched group in the search, instead of \1.
- Example: "abbc".replace(/(.)\1/g, "$1") => "abc"
| is magic, \| is literal
( is magic, \( is literal

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Examples

Matching
- string = "Hello world!".match(/world/);
- stringArray = "Hello world!".match(/l/g); // Matched strings are returned in a string array
- "abc".match(/a(b)c/)[1] => "b" // Matched subgroup is the second member (having the index "1") of the resulting array
Replacement
- string = string.replace(/expression without quotation marks/g, "replacement");
- string = string.replace(/escape the slash in this\/way/g, "replacement");
- string = string.replace( ... ).replace ( ... ). replace( ... );
Test
- if (string.match(/regexp without quotation marks/)) {

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Modifiers

Modifier	Note
g	Global. The list of matches is returned in an array.
i	Case-insensitive search
m	Multiline. If the operand string has multiple lines, ^ and $ match the beginning and end of each line within the string, instead of matching the beginning and end of the whole string only. "a\nb\nc".replace(/^b$/g,"d") => "a\nb\nc" "a\nb\nc".replace(/^b$/gm,"d") => "a\nd\nc"

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Operators

Operator	Effect
\b	Matches boundary of a word.
\w	Matches an alphanumeric character, including "_".
\W	Negation of \w.
\s	Matches a whitespace character (space, tab, newline, formfeed)
\S	Negation of \s.
\d	Matches a digit.
\D	Negation of \d.