JavaScript defines a datatype known as a regular expression for describing and matching patterns in strings of text. RegExps are not one of the fundamental data types in JavaScript, but they have a literal syntax like numbers and strings do, so they sometimes seem like they are fundamental.
A regular expression is a pattern of characters.
Syntax :
/pattern/modifiers;
var str = /^b…m$/
The above code defines a RegEx pattern. The pattern is: any five letter string starting with b and ending with m.
| String | Matched |
| bm | No match |
| byuetm | No match |
| btm | No match |
| bwdem | match |
There are two ways you can create a regular expression in JavaScript.
1) Using a regular expression literal
The regular expression consists of a pattern enclosed between slashes /
cost str = /xyz/;
Here /xyz/ is an regular expression.
2) Using the RegExp() constructor function
You can also create a regular expression by calling the RegExp() constructor Function.
const str = new Str('xyz');
MetaCharacters
Metacharacters are characters that are interpreted in a special way by a RegEx engine. Here's a list of metacharacters:
[ ]. ^ $ * + ? { } ( ) \ |
[] - Square brackets
| Expression | String | Matched |
| [abc] | a | 1 match |
| [abc] | ab | 2 match |
| [abc] | abx | 2 match |
| [abc] | xyz | No match |
| [abc] | aaa | 3 match |
. - Period
A period matches any single character (except newline '\n').
| Expression | String | Matched |
| .. | x | No match |
| .. | xy | 1 match |
| .. | xyz | 1 match |
| .. | xyzw | 2 match |
^ - Caret
The caret symbol ^ is used to check if a string starts with a certain character.
| Expression | String | Matched |
| ^x | x | 1 match |
| ^x | pqr | No match |
| ^x | abc | No match |
| ^x | xy | 1 match |
$ - Dollar
The dollar symbol $ is used to check if a string ends with a certain character.
| Expression | String | Matched |
| x$ | x | 1 match |
| x$ | abx | 1 match |
| x$ | bnc | No match |
