Regular Expressions are a concise method of describing text patterns. In JavaScript a Regular Expression are also special objects that can be used with some methods to help find or transform text.

Defining a Regular Expression:``

1. let r = /ab+c/ constructing with slashes.
2. let r = new RegExp('ab+c') constructing with the constructor function ‘RegExp’.

Special Characters

Regular Expression use a bunch of special characters to express pattern matches.

Character	meaning	example
^	Matches beginning of input
$	Matches end of input
*	Matches preceding expression 0 or more times
+	Matches preceding expression 1 or more times
?	Matches preceding expression 0 or 1 times
.	Matches any single character except newline
{n}	Matches exactly ’n’ occurrences of the preceding expression	/b{3}/
n,	Matches at least ’n’ occurrences of the preceding expression	/b{3,}/
n,m	Matches at least ’n’ and at most ’m’ occurrences of the preceding expression	/b{3,}/
[abc]	Matches any one of ‘a’ or ‘b’ or ‘c’
[^abc]	Matches anything not ‘a’ or ‘b’ or ‘c’
\b	Matches a word boundary
\B	Matches a non-word boundary
\d	Matches a digit character	same as [0-9]
\D	Matches a non-digit character	same as [^0-9]
\s	Matches a white space character
\S	Matches a non-white space character
\w	Matches any alphanumeric character	same as [A-Za-z0-9_]
\W	Matches any alphanumeric character	same as [^A-Za-z0-9_]
|	or ie. matches ‘a’ or ‘b’	a | b
(x)	matches ‘x’ and remembers the match
(?:x)	matches ‘x’ but does not rember the match

Regular expression flags

flags for regular expression change the search matching.

g - global search

i - case-insensitive

m - multi-line

u - unicode

y - sticky (starts with the current position in the target string)

Other sites about Regular Expressions

• Regular Expression Tester