JavaScript Regular Expression Object

The RegExp Object

It is used to validate a pattern of characters.

How to define a regular expression

1.       Using RegExp objects constructor function.

2.       Using literal.

Using RegExp: var regularexpression = new RegExp(“pattern”,”flag”);

Using literal: /pattern/flag

Types of flags in JavaScript

1.       g- finds all matches globally

2.       i- ignores the case in searches, i.e. text written in lowercase is same as uppercase.

3.       m- represents multiline matching, i.e. the symbol caret(^) and dollar($) match the beginning  and end of the line as well as entire string.

Patterns used in the RegExp object

Pattern delimiters:

Pattern	Description
(pattern),(?:pattern)	Matches the entire contained pattern
	(pattern) retains the match
	(?:pattern) does not retain the match

Lookaheads

Pattern	description
(?=pattern),(?!pattern)	(?=pattern) matches only if the condition is satisfied
	(?!pattern) matches only if the condition is not satisfied

Character Escapes

Pattern	Description
\f	Matches form feed
\r	Matches carriage return
\n	Matches linefeed
\t	Matches horizontal tab
\v	Matches vertical tab
\0	Matches null character
[\b]	Matches back space
\s	Matches whitespace
\S	Matches anything but a whitespace
\w	Matches any alphanumerical character including underscore
\W	Matches any non-word character
\d	Matches any digit
\D	Matches any non-digit
\b	Matches a word boundary
\B	Matches a non-word boundary
\cX	Matches a control character. Example g:\cd matches control-d
\xhh	Matches the character with two characters with hexadecimal code hh
\uhhh	Matches the Unicode character with four characters of hexadecimal code hhhh

Character Sets

Pattern	Description
[character],[^character]	[character] matches all the contained character
	[^character] matches all but the contained characters

List of Quantifiers of the RegExp Object

Quantifier	Description
n+	Represents a string which contains at least one n
n*	Represents a string that contains zero or more occurrences of n
n?	Represents a string that contains zero or one occurrences of n
n{a}	Represents a string that contains n, a number of times
n{a,b}	Represents a string that contains n, a to b number of times
n{a,}	Represents a string that contains n, a or more number of times
n$	Represents a string that ends with n
^n	Represents a string that starts with a
?=n	Represents a string that is followed by specific string  n
?!n	Represents a string that is not followed by specific string n

Properties of RegExp Object

Property	Description
global	Refers that the g modifier is set
ignoreCase	Refers that the I modifier is set
lastIndex	Refers the index to start the next match
multiline	Refers that the m modifier is set
source	Refers the text of RegExp pattern

Methods of RegExp object

Method	Description
compile	Compiles the RegExp object
exec	Tests for the match in a string and returns a result array
test	Tests for a match in a string and returns true or false