Javascript’s RegExp

RegExp object

Javascript has an Object which compiles Regular Expressions into a Finite State Machine

The F.S.M. is internal, and is stored in the RegExp object

var g = new RegExp;

RegExp object

uses extended grep as the language (which are typically referred to as Regular Expressions)

Compile the expression order to use it

RegExp object

new RegExp(”grep_string”, “options”);

Using it is FAST, which is why grep patterns are so popular

Creating/compiling the RegExp object is SLOW!

RegExp Options

Optional parameter (flags):

...new RegExp(”string”, “ig”)

regExpObj.compile(”string”, “gi”);

i= ignore case

g= global (find every match)

allows replace all + useful in loops

RegExp object

re= new RegExp( /querystring/ );

re.test( “someText” );

re.exec( “someText” );

returns an array of results

[0] is found string

[>=1] is found parts() in that string

Alternate Methods

Some browsers promote 1 method over another

var x = new RegExp(”string”);

vs (preferred)

var x = new RegExp(/string/);

vs (not recommended but shortest)

var x= /string/;

RegExp Options

multiline problem

m=multiline flag is NOT supported

multiline is a global boolean property of RegExp object itself

if not supported; you can test for it.

if( typeof(RegExp.multiline) == ‘Boolean’)

/Common Use/

/string/ similar to “quotes” on strings

if you use “string” you must escape:

/\d\d/ (match 2 digit pattern)

vs

“\\d\\d” (match 2 digit string)

Example

var re = new RegExp(”GREP”, “i”);

var str = “stringrep”;

if( re.test(str) )

alert(“found it!”);

Example 2

var re = /grep/i ;

var str = “stringrep”;

if( re.test(str) )

alert(“found it!”);

String Object

.search(regexp)

returns position found or -1

.replace(regexp, string)

returns new string or old string

.match(regexp)

returns array of matches or null

Example

var g = new RegExp(”grep”, “i”);

var str = “stringrep”;

if( str.search(g) )

alert(“found it!”);

Example 2

Preferred modern syntax:

var str = “stringrep”;

if( str.search( /grep/ ) )

alert(“found it!”);

Learning

Use a Text Editor that supports RegExp or Grep Patterns (even better if it claims Perl Reg. Exp.)

Use the Regular Expression Play Pen webpage (class website)

Use javascript (code, make your own test page, or javascript console)