A regular expression is a sequence of characters that forms a search pattern.
When you search for data in a text, you can use this search pattern to describe what you are searching for.
A regular expression can be a single character, or a more complicated pattern.
Regular expressions can be used to perform all types of text search and text replace operations.
Syntax
/pattern/modifiers;Example
var patt = /Mytat/i;Example explained:
/Mytat/i is a regular expression.
Mytat is a pattern (to be used in a search).
i is a modifier (modifies the search to be case-insensitive).
Using String Methods
In JavaScript, regular expressions are often used with the two string methods: search() and replace().
The search() method uses an expression to search for a match, and returns the position of the match.
The replace() method returns a modified string where the pattern is replaced.
Using String search() With a String
The search() method searches a string for a specified value and returns the position of the match:
Example
Use a string to do a search for "Mytat" in a string:var n = str.search("Mytat");
Using String search() With a Regular Expression
Example
Use a regular expression to do a case-insensitive search for "mytat" in a string:
var n = str.search(/mytat/i);
The result in n will be:
6
Using String replace() With a String
The replace() method replaces a specified value with another value in a string:
var res = str.replace("Microsoft", "Mytat");
Use String replace() With a Regular Expression
Example
Use a case insensitive regular expression to replace Microsoft with mytat in a string:
var res = str.replace(/microsoft/i, "Mytat");
The result in res will be:
Visit Mytat!
Regular Expression Modifiers
Modifiers can be used to perform case-insensitive more global searches:
| 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 |
Regular Expression Patterns
Brackets are used to find a range of characters:
| Expression | Description |
|---|---|
| [abc] | Find any of the characters between the brackets |
| [0-9] | Find any of the digits between the brackets |
| (x|y) | Find any of the alternatives separated with | |
Metacharacters are characters with a special meaning:
| Metacharacter | Description |
|---|---|
| \d | Find a digit |
| \s | Find a whitespace character |
| \b | Find a match at the beginning of a word like this: \bWORD, or at the end of a word like this: WORD\b |
| \uxxxx | Find the Unicode character specified by the hexadecimal number xxxx |
Quantifiers define quantities:
| Quantifier | Description |
|---|---|
| n+ | Matches any string that contains at least one n |
| n* | Matches any string that contains zero or more occurrences of n |
| n? | Matches any string that contains zero or one occurrences of n |
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