JavaScript RegExp tutorial

 

A regular expression refers to the object which represents the pattern of characters.

JavaScript provides the RegEx class which provides the pattern-matching and search-and-replace functionality on text.

Syntax

/pattern/modifiers;

 

Modifiers

Modifiers are used to perform case-insensitive and global searches.

Modifier Description
g It is used to find all matches.
i It is used to perform case-insensitive matching
m It is used to perform multi line matching.

Brackets

Brackets are used to find the range of characters.

Expression Description
[abc] It is used to find any character between the brackets.
[^abc] It is used to find any character not between the brackets.
[0-9] It is used to find any character between the brackets (any digit).
[^0-9] It is used to find any character not between the brackets (any non-digit)
(x|y) It is used to find any of the alternatives specified.

 

Metacharacters

Metacharacters are the alphabetical characters preceded by a backslash with a special meaning.

Metacharacter Description
. It is used to find a single character. It exclude newline or line terminator
\w It is used to find a word character.
\W It is used to find a non-word character.
\d It is used to find a digit.
\D It is used to find a non-digit character.
\s It is used to find a white space character.
\S It is used to find a non-white space character.
\b It is used to find a match at the beginning/end of a word.
\B It is used to find a match not at the beginning/end of a word.
\0 It is used to find a NULL character.
\n It is used to find a new line character.
\f It is used to find a form feed character.
\r It is used to find a carriage return character.
\t It is used to find a tab character.
\v It is used to find a vertical tab character.
\xxx It is used to find the character specified by an octal number xxx.
\xdd It is used to find the character specified by a hexadecimal number dd.
\udddd It is used to find  the Unicode character specified by a hexadecimal number dddd.

Quantifiers

Quantifier Description
n+ It matches any string that contains at least one n.
n* It matches any string that contains zero or more occurrences of n.
n? It matches any string that contains zero or one occurrences of n.
n{X} It matches any string that contains a sequence of X n‘s.
n{X,Y} It matches any string that contains a sequence of X to Y n‘s.
n{X,} It matches any string that contains a sequence of at least X n‘s.
n$ It matches any string with n at the end of it.
^n It matches any string with n at the beginning of it.
?=n It matches any string that is followed by a specific string n.
?!n It matches any string that is not followed by a specific string n.

RegExp Object Properties

Property Description
constructor It returns the function that created the RegExp object’s prototype.
global It used to check whether the “g” modifier is set.
ignoreCase It used to check whether the “i” modifier is set.
lastIndex It is used to get the index at which to start the next match.
multiline It used to check whether the “m” modifier is set.
source It is used to get the text of the RegExp pattern.

RegExp Object Methods

RegExp.exec() Method:
Use: To get an array containing all the matched groups for a specified string.

RegExp.test() Method:
Use: To search a match between a regular expression and a specified string.

RegExp.toString() Method:
Use: To retrieve a string to represent the regular expression.

Example

<!DOCTYPE html>
<html>
<body>
<script>
var string  = "HELLO WORLD";  
var regExObj = new RegExp( "HELLO", "g" );  
var print = regExObj.exec(string);  
document.write("Returned value : " +  print);   
</script>
</body>
</html>

Output

Returned value : HELLO
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