(x)

It matches x & remembers the match, which are access by RegExp.$N, where N is any positive number

• The number of '(x)' used in your regular expression is the maximum value of 'N' (but limited till 9) you can access

• Note! If more than 9 '(x)' used then we will access them with the help of exec() covered under RegExp methods

For example :

library_booksvar str = "black book";
var pattern = /(b.)./g;
alert(str.match(pattern));
// Output: bla,boo
alert(RegExp.$1);
// Output: bo

Matches: black book

Comment : RegExp.$1 remembers the last match via (b.) which is 'bo' in above case

library_booksRegExp.$N   // 10 > N > 0

library_booksRegExp.$N.length

library_booksRegExp.$N[index]  // index starts from 0

(?:x)

It matches x but don't remember the match

For example :

library_booksvar str = "black book";
var pattern = /(?:b.)./g;
alert(str.match(pattern));
// Output: bla,boo
alert(RegExp.$1);
// Output: 

Matches: black book

Comment : It doesn't remember match via (?:b.)

x|y

It matches either x or y

• Use (x|y) format if you have to integrate with other characters, like: /a(b|c|d)/ looks for 'ab' or 'ac' or 'ad'

For example :

library_booksvar str = "black book, red book";
var pattern = /black|red/g;
alert(str.match(pattern));
// Output: black,red

Matches: black book, red book

\N

It holds the reference of the match value by (x), where N is any positive number

For example :

library_booksvar str = "pen! yes,paper! yes,book! no";
var pattern = /pen(! )(yes,)paper\1\2/g;
alert(str.match(pattern));
// Output: pen! yes,paper! yes,

Matches: pen! yes,paper! yes,book! no

Comment : \1 means same value matched by (! )
                     \2 means same value matched by (yes,)