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RegExp constructor

Regular expressions creation.

Description

In JavaScript regular expressions are created using the constructor RegExP or created using literal format.

Syntax


Signature Description
var aRegExp = new RegExp(pattern [, flags]);Creates a wrapper object using the constructor RegExP.
var bRegExp = /pattern/flags;Creates a wrapper object using literal format.

Parameters


Parameter Description
patternThe regular expression pattern.
flagsFlags can be used individually or in combination and are applied to the characters we are searching with the regular expression pattern.
  • g - global match - finds all matches rather than stopping after a match.
  • i - ignore case - case insensitive match.
  • m - line match - match each line.

Class Properties


Class Property Description
prototypeEnables property assignment to objects of type RegExp.

Instance Properties


Instance Property Description
constructorReturns a reference to the RegExp function that created the prototype.
globalReturns true if global match flag set or false otherwise.
ignoreCaseReturns true if ignore case flag set or false otherwise.
lastIndexIndex to start next match from.
multilineReturns true if match each line flag set or false otherwise.
sourceReturns the text of the pattern.

Class Methods

None.

Instance Methods


Instance Method Description
Getter (Accessor) MethodsThese methods DO NOT modify the Regexp object
exec()Returns a result array, or null from an executed search in a specified string.
test()Returns true or false for a match between a regular expression and a string.
toString()Returns a string representation of the RegExp object.
Setter (Mutator) MethodsThese methods DO modify the Regexp object
None.

Special Character Usage In Regular Expressions


Character Meaning Examples
Escape/Unescape
\ Used to escape characters that are treated literally within regular expressions or alternatively to unescape special characters Literal Content
/d/ matches the character d
/\d/ matches a digit character

Unescape Special Characters
/d+/ matches one or more character d
/d\+/ matches d+
Quantifiers
* Matches preceding item 0 or more times /do*/
Every dig has its day
Every dog has its day
Shut that doooor
Can you see me
? Matches preceding item 0 or 1 times /do?/
Every dig has its day
Every dog has its day
Shut that doooor
Can you see me
+ Matches preceding item 1 or more times /do+/
Every dig has its day
Every dog has its day
Shut that doooor
Can you see me
^ Matches beginning of input
If line match flag (m) is set will also match after a line break character.
/^A/
an Armadillo
An Armadillo
$ Matches end of input
If line match flag (m) is set will also match before a line break character.
/Z$/
BuzZ BuZz
BuzZ BuZZ
x(?=y) Matches Regexp(x) only if followed by y /and(?= five)/
one and two and three
one and two and four
one and two and five
x(?!y) Matches Regexp(x) only if NOT followed by y /and(?! five)/
one two and three
one two and four
one two and five
{n} Matches exactly n occurrences of the preceding item.
Where n is a positive integer
/o{4}/
one two
one twoo
one twooo
one twoooo
{n,} Matches at least n occurrences of the preceding item.
Where n is a positive integer
/o{3,}/
one two
one twoo
one twooo
one twoooo
{n,m} Matches at least n and at most m occurrences of the preceding item.
Where n and m are positive integers
/o{2,3}/
one two
one twoo
one twooo
one twoooo
Special Characters
. Matches any single character except newline characters. /.t/
This Time tonight
this is good
x|y Matches x or y /three|four/
one two
one two three
one two four
[xyz] A character set.
Matches any of the enclosed characters.
You can specify a range of characters by using a hyphen.
/[eno]/g
one two
one twoo
one twooo
one twoooo
[^xyz] A negated character set.
Matches anything not enclosed in the brackets.
You can specify a range of characters by using a hyphen.
/[^eno]/g
one two
one twoo
one twooo
one twoooo
\b Find a match at the beginning or end of a word. At Beginning
/\bday/g
the day today is saturday
daytime and nighttime

At End
/day\b/g
the day today is saturday
day and nighttime
\B Find a match NOT at the beginning or end of a word. Not At Beginning
/\Bday/g
the day today is saturday
daytime and nighttime

Not At End
/day\B/g
the day today is saturday
day and nighttime
\d Find a digit character.
Same as the range check [0-9].
/\d/g/
Was it 76 or 77
\D Find a non-digit character.
Same as the range check [^0-9].
/\D/g/
Was it 76 or 77
\0 Find a Nul character.
Do not follow this regualr expression with another digit
/\0/
\s Find a whitespace character. Example below words are greyed out and spaces are highlighted in red purely for emphasis
/\s/g/
Beware of the dog
\S Find a non-whitespace character. Example below spaces are grayed out for emphasis
/\S/g/
Beware of the dog 
\w Find a word character.
A word character is a character in ranges a-z, A-Z, 0-9 and also includes the _ (underscore) symbol.
Same as the range check [A-Za-z0-9_].
/\w/g/
76% off_sales. £12 only
\W Find a non-word character.
Same as the range check [^A-Za-z0-9_].
/\W/g/
76% off_sales. £12 only
\xnn Find a character that equates to hexadecimal nn.
Where nn is a two digit hexadecimal number
/\x70/
The quick brown fox jumps.
\unnnn Find a character with the unicode value nnnn.
Where nnnn is a four digit hexadecimal number
/\u0065/
The quick brown fox jumps.
Control Characters
[\b] Find a backspace character. /[\b]/
Will search for backspace.
The brackets differentiate this from \b special character
\cA Find a control character A.
Where A is the control character in range A-Z you are looking for.
/\cC/
Will search for control-C in a string.
\f Find a formfeed character. /\f/
When matched will return the formfeed character

When searched will return the zero-based index position the formfeed character was found in.
\n Find a newline character. /\n/
When matched will return the newline character

When searched will return the zero-based index position the newline character was found in.
\r Find a carriage return character. /\r/
When matched will return the carriage return character

When searched will return the zero-based index position the carriage return character was found in.
\t Find a tab character. /\t/
When matched will return the tab character

When searched will return the zero-based index position the tab character was found in.
\v Find a vertical tab character. /\v/
When matched will return the vertical tab character

When searched will return the zero-based index position the vertical tab character was found in.

Related Tutorials

JavaScript Intermediate Tutorials - Lesson 9 - Regular Expressions



  

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