JavaScript Regular Expressions

RegExp, is short for regular expression.

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Complete RegExp Object Reference

For a complete reference of all the properties and methods that can be used with the RegExp object:

Go to our complete RegExp object reference.

The reference contains a brief description and examples of use for each property and method!

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What is RegExp?

A regular expression is an object that describes a pattern of characters.

When you search in a text, you can use a pattern to describe what you are searching for.

A simple pattern can be one single character.

A more complicated pattern can consist of more characters, and can be used for parsing, format checking, substitution and more.

Regular expressions are used to perform powerful pattern-matching and "search-and-replace" functions on text.

Syntax

var patt=new RegExp(pattern,modifiers);

or more simply:

var patt=/pattern/modifiers;

• pattern specifies the pattern of an expression
• modifiers specify if a search should be global, case-sensitive, etc.

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RegExp Modifiers

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

The i modifier is used to perform case-insensitive matching.

The g modifier is used to perform a global match (find all matches rather than stopping after the first match).

Example 1

Do a case-insensitive search for "w3schools" in a string:

var str = "Visit W3Schools";
var patt = /w3schools/i;

The marked text below shows where the expression gets a match:

Visit W3Schools

Try it Yourself »

Example 2

Do a global search for "is":

var str = "Is this all there is?";
var patt = /is/g;

The marked text below shows where the expression gets a match:

Is this all there is?

Try it Yourself »

Example 3

Do a global, case-insensitive search for "is":

var str = "Is this all there is?";
var patt = /is/gi;

The marked text below shows where the expression gets a match:

Is this all there is?

Try it Yourself »

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test()

The test() method searches a string for a specified value, and returns true or false, depending on the result.

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

Example

var patt = new RegExp("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

Try it Yourself »

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exec()

The exec() method searches a string for a specified value, and returns the text of the found value.

If no match is found, it returns null.

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

Example 1

var patt = new RegExp("e");
patt.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

Try it Yourself »

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Complete RegExp Reference

For a complete reference, go to our Complete JavaScript RegExp Reference.

The reference contains descriptions and examples of all RegExp properties and methods.