YouTip

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RegExp Object

Regular expressions are objects that describe character patterns.

Regular expressions are used for pattern matching and search/replace on strings. They are a powerful tool for performing pattern matching on strings.

Syntax

var patt=new RegExp(pattern,modifiers);

Or a simpler way:

var patt=/pattern/modifiers;

• pattern describes the pattern of the expression
• modifiers are used to specify global matching, case-insensitive matching, and multiline matching

Note: When using the constructor to create a regular expression object, normal character escape rules apply (prepend with backslash ). For example, the following are equivalent:

var re = new RegExp("\w+");var re = /w+/;

For more about the RegExp object, please read our JavaScript RegExp Object Tutorial.

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Modifiers

Modifiers are used to perform case-insensitive and global matching:

Modifier	Description
i	Perform case-insensitive matching.
g	Perform global matching (find all matches rather than stopping after the first match).
m	Perform multiline matching.

Brackets

Brackets are used to find characters within a range:

Expression	Description
	Find any character between the brackets.
[^abc]	Find any character not between the brackets.
	Find any digit from 0 to 9.
	Find any character from lowercase a to lowercase z.
	Find any character from uppercase A to uppercase Z.
	Find any character from uppercase A to lowercase z.
	Find any character within the given set.
[^adgk]	Find any character outside the given set.
(red|blue|green)	Find any of the specified options.

Metacharacters

Metacharacters are characters with special meanings:

Metacharacter	Description
.	Find a single character, except newline or line terminator.
w	Find word characters (digits, letters, underscore).
W	Find non-word characters.
d	Find digits.
D	Find non-digit characters.
s	Find whitespace characters.
S	Find non-whitespace characters.
b	Match a word boundary.
B	Match a non-word boundary.
	Find the NULL character.
n	Find a newline character.
f	Find a form feed character.
r	Find a carriage return character.
t	Find a tab character.
v	Find a vertical tab character.
xxx	Find the character specified by octal number xxx.
xdd	Find the character specified by hexadecimal number dd.
uxxxx	Find the Unicode character specified by hexadecimal number xxxx.

Quantifiers

Quantifier	Description
n+	Matches any string that contains at least one n. For example, /a+/ matches the "a" in "candy", and all "a"s in "caaaaaaandy".
n*	Matches any string that contains zero or more occurrences of n. For example, /bo*/ matches "boooo" in "A ghost booooed", "b" in "A bird warbled", but not "A goat grunted".
n?	Matches any string that contains zero or one occurrence of n. For example, /e?le?/ matches "el" in "angel" and "le" in "angle".
n{X}	Matches a sequence of X occurrences of n. For example, /a{2}/ does not match the "a" in "candy", but matches the two "a"s in "caandy", and the first two "a"s in "caaandy".
n{X,}	X is a positive integer. Matches when the preceding pattern n occurs at least X times consecutively. For example, /a{2,}/ does not match "a" in "candy", but matches all "a"s in "caandy" and "caaaaaaandy".
n{X,Y}	X and Y are positive integers. Matches when the preceding pattern n occurs at least X times and at most Y times consecutively. For example, /a{1,3}/ does not match "cndy", matches "a" in "candy", two "a"s in "caandy", and the first three "a"s in "caaaaaaandy". Note that when matching "caaaaaaandy", even though the original string has more "a"s, the match is "aaa".
n$	Matches any string that ends with n.
^n	Matches any string that starts with n.
?=n	Matches any string that is immediately followed by the specified string n.
?!n	Matches any string that is not immediately followed by the specified string n.

RegExp Object Methods

Method	Description
compile	Deprecated in version 1.5. Compiles a regular expression.
exec	Retrieves the specified value in the string. Returns the found value and determines its position.
test	Retrieves the specified value in the string. Returns true or false.
toString	Returns the string representation of the regular expression.

String Object Methods Supporting Regular Expressions

Method	Description	FF	IE
search	Retrieves the value that matches the regular expression.	1	4
match	Finds one or more matches of the regular expression.	1	4
replace	Replaces substrings that match the regular expression.	1	4
split	Splits a string into an array of strings.	1	4

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RegExp Object Properties

Property	Description
constructor	Returns a function that is the prototype for creating RegExp objects.
global	Checks whether the "g" modifier is set.
ignoreCase	Checks whether the "i" modifier is set.
lastIndex	Specifies the starting position for the next match.
multiline	Checks whether the "m" modifier is set.
source	Returns the matching pattern of the regular expression.

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