Introduction
Regular Expression is a very important part of any language programming because of its ability to help programmers to write fast and pure applications.
You Don't Know What a Regular Expression Is?
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.
Web developer can also use Regular Expression in JavaScript. Now I describe some simple examples of using Regular Expression in JavaScript.
The overall syntax should look like:
/pattern/modifiers
- pattern specifies the search pattern
- modifiers specify if our search should be case-sensitive, global, etc.
Modifiers Table
| Modifier | Description |
| i | Perform case-insensitive matching |
| g | Perform a global match (find all matches rather than stopping after the first match) |
| m | Perform multiline matching |
To compile and use Regular Expression, you can use three useful functions.
Regular Expression Object Methods
| Method | Description |
compile() | Compiles a regular expression |
exec() | Tests for a match in a string. Returns the first match |
test() | Tests for a match in a string. Returns true or false |
Character Escapes (Metacharacters)
| Metacharacter | Description |
| . | Find a single character, except newline or line terminator |
| \w | Find a word character |
| \W | Find a non-word character |
| \d | Find a digit |
| \D | Find a non-digit character |
| \s | Find a whitespace character |
| \S | Find a non-whitespace character |
| \b | Find a match at the beginning/end of a word |
| \B | Find a match not at the beginning/end of a word |
| \0 | Find a NUL character |
| \n | 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 |
| \xxx | Find the character specified by an octal number xxx |
| \xdd | Find the character specified by a hexadecimal number dd |
| \uxxxx | Find the Unicode character specified by a hexadecimal number xxxx |
Metacharacter table from W3Schools.
Example
Test sentence: Sometext sometext sometext
| Expression | Test Result |
| /sometext/ | Sometext sometext sometext |
| /sometext/i | Sometext sometext sometext |
| /sometext/g | Sometext sometext sometext |
| /sometext/gi | Sometext sometext sometext |
| /some/ | Sometext sometext sometext |
| /some/i | Sometext sometext sometext |
| /some/g | Sometext sometext sometext |
| /some/ig | Sometext sometext sometext |
It's easy!
In the next article, I will show you Regular Expression performance in some cases and also how to make simple and pure Regular Expressions.
History
- 19 May, 2011: Initial version.
- 1 June, 2011: Added sample source code.
- 16 July, 2012: Add metacharacters table.
