Regular Expression in Javascript

Regular Expression are very important in professional JavaScript.

There is a wonderful
Resource in Mozilla Developer Center.

Two ways to construct a regular expression

1. Literal expression

 
Re =/AB + C/g;
 

2. constructor Function

 
Re = new Regexp ("AB + C", "G ");
 

Possible flags

1. G-global search.

2. I-case-insensitive search.

3. M-multi-line search.

Simple and special characters

A regular expression is composed of simple characters (such as/ABC123 _/) and special
Characters.

Some important special characters:

1. ^-matches beginning of input.

2. $-matches end of input.

3. *-matches the preceding character 0 or more times.

4. +-matches the preceding character 1 or more times.

5 .? -Matches the preceding character 0 or 1 time.

6 ..-matches any single character.

Sepcial character \

There are two meanings of the special charater.

1. used before simple character, indicating that the next character is special.

E.g. B is a simple character, \ B is used to indicate a word
Boundary.

Some important special character \:

1. \ B-matches a word boundary.

2. \ D-matches a digit character.

3. \ s-matches a white space character, including space,
Tab, line feed.

4. \ W-matches any alphanumeric character including
Underscore. equivalent to [A-Za-z0-9 _].

Javascript funtions to operate regular expression

1. Exec-returns: array.

2. Match-returns: array or null.

3. Test-returns: true or false.

4. Search-returns: Index or-1.

5. replace-returns: string.

Examples:

 
/D (B +) D/g.exe C ("cdbbdbsbz"); // ["dbbd", "BB"] "cdbbdbsbz ". match (/d (B +) D/g); // ["dbbd"] "cdbbdbsbz ". search (/d (B +) D/g); // 1/D (B +) D/g. test ("cdbbdbsbz"); // true