Tuesday, March 15, 2011

JavaScript RegExp for Validation

A regular expression is an object that describes a pattern of characters.
Regular expressions are used to perform pattern-matching and "search-and-replace" functions on text.

Syntax

var patt=new RegExp(pattern,modifiers);

or more simply:

var patt=/pattern/modifiers;
  • pattern specifies the pattern of an expression
  • modifiers specify if a search should be global, case-sensitive, etc.

Modifiers

Modifiers are used to perform case-insensitive and global searches:
Modifier
Description
Perform case-insensitive matching
Perform a global match (find all matches rather than stopping after the first match)
m
Perform multiline matching

Brackets

Brackets are used to find a range of characters:
Expression
Description
Find any character between the brackets
Find any character not between the brackets
[0-9]
Find any digit from 0 to 9
[A-Z]
Find any character from uppercase A to uppercase Z
[a-z]
Find any character from lowercase a to lowercase z
[A-z]
Find any character from uppercase A to lowercase z
[adgk]
Find any character in the given set
[^adgk]
Find any character outside the given set
(red|blue|green)
Find any of the alternatives specified

Metacharacters

Metacharacters are characters with a special meaning:
Metacharacter
Description
Find a single character, except newline or line terminator
Find a word character
Find a non-word character
Find a digit
Find a non-digit character
Find a whitespace character
Find a non-whitespace character
Find a match at the beginning/end of a word
Find a match not at the beginning/end of a word
\0
Find a NUL character
Find a new line character
\f
Find a form feed character
\r
Find a carriage return character
\t
Find a tab character
\v
Find a vertical tab character
Find the character specified by an octal number xxx
Find the character specified by a hexadecimal number dd
Find the Unicode character specified by a hexadecimal number xxxx

Quantifiers

Quantifier
Description
Matches any string that contains at least one n
Matches any string that contains zero or more occurrences of n
Matches any string that contains zero or one occurrences of n
Matches any string that contains a sequence of X n's
Matches any string that contains a sequence of X to Y n's
Matches any string that contains a sequence of at least X n's
Matches any string with n at the end of it
Matches any string with n at the beginning of it
Matches any string that is followed by a specific string n
Matches any string that is not followed by a specific string n

RegExp Object Properties

Property
Description
Specifies if the "g" modifier is set
Specifies if the "i" modifier is set
The index at which to start the next match
Specifies if the "m" modifier is set
The text of the RegExp pattern

RegExp Object Methods

Method
Description
Compiles a regular expression
Tests for a match in a string. Returns the first match
Tests for a match in a string. Returns true or false

test()

The test() method searches a string for a specified value, and returns true or false, depending on the result.
The following example searches a string for the character "e":

Example

var patt1=new RegExp("e");
document.write(patt1.test("The best things in life are free"));

Since there is an "e" in the string, the output of the code above will be:
true

exec()

The exec() method searches a string for a specified value, and returns the text of the found value. If no match is found,
it returns null.

The following example searches a string for the character "e":

Example 1

var patt1=new RegExp("e");
document.write(patt1.exec("The best things in life are free"));

Since there is an "e" in the string, the output of the code above will be:
e

You can read this from www.w3schools.com.

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