A regular expression is a sequence of characters that forms a search pattern.

The search pattern can be used for text search and text replace operations.

What Is a Regular Expression?

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 = /w3schools/i

Example explained:

/w3schools/i is a regular expression.

w3schools 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 Regular Expression

Example

Use a regular expression to do a case-insensitive search for "w3schools" in a string:

var str = "Visit W3Schools";

var n = str.search(/w3schools/i);

The result in n will be:

6

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Using String search() With String

The search method will also accept a string as search argument. The string argument will be converted to a regular expression:

Example

Use a string to do a search for "W3schools" in a string:

var str = "Visit W3Schools!";

var n = str.search("W3Schools");

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Use String replace() With a Regular Expression

Example

Use a case insensitive regular expression to replace Microsoft with W3Schools in a string:

var str = "Visit Microsoft!";

var res = str.replace(/microsoft/i, "W3Schools");

The result in res will be:

Visit W3Schools!

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Using String replace() With a String

The replace() method will also accept a string as search argument:

var str = "Visit Microsoft!";

var res = str.replace("Microsoft", "W3Schools");

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Did You Notice?

Regular Expression Modifiers

Modifiers can be used to perform case-insensitive more global searches:

Regular Expression Patterns

Brackets are used to find a range of characters:

Metacharacters are characters with a special meaning:

Quantifiers define quantities:

Using the RegExp Object

In JavaScript, the RegExp object is a regular expression object with predefined properties and methods.

Using test()

The test() method is a RegExp expression method.

It searches a string for a pattern, and returns true or false, depending on the result.

The following example searches a string for the character "e":

Example

var patt = /e/;

patt.test("The best things in life are free!");

Since there is an "e" in the string, the output of the code above will be:

true

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You don't have to put the regular expression in a variable first. The two lines above can be shortened to one:

/e/.test("The best things in life are free!")

Using exec()

The exec() method is a RegExp expression method.

It searches a string for a specified pattern, and returns the found text.

If no match is found, it returns null.

The following example searches a string for the character "e":

Example 1

/e/.exec("The best things in life are free!");

Since there is an "e" in the string, the output of the code above will be:

e

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JavaScript RegExp Reference

RegExp Object

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.

Syntax

/pattern/modifiers;

Example:

var patt = /w3schools/i

Example explained:

• /w3schools/i is a regular expression.
• w3schools is a pattern (to be used in a search).
• i is a modifier (modifies the search to be case-insensitive).

For a tutorial about Regular Expressions, read our JavaScript RegExp Tutorial.

Modifiers

Modifiers are used to perform case-insensitive and global searches:

Brackets

Brackets are used to find a range of characters:

Metacharacters

Metacharacters are characters with a special meaning:

Quantifiers

RegExp Object Properties

RegExp Object Methods