JavaScript Regular Expressions

Regular expressions are the character sequence that constitutes

This search pattern can be used for text search and text replacement operations.

What is a regular expression?

Regular expressions are the constituentSearch pattern (search pattern)character sequence.

When you search for data in text, you can use search patterns to describe what you are searching for.

Regular expressions can be a single character, or a more complex pattern.

Regular expressions can be used to perform all types ofText searchandText replacementoperation.

syntax

/pattern/modifiers;

Example

var patt = /codew3c/i;

Example explanation:

/codew3c/i is a regular expression.

codew3c is the pattern (pattern) used in the search).

i are modifiers (change the search to case-insensitive).

Use the string method

In JavaScript, regular expressions are commonly used in twoString methods:search() and replace().

search() The method uses the expression to search for matches and then returns the position of the match.

replace() The method returns the modified string where the pattern was replaced.

Use the string method search() to process the string

search() The method also accepts a string as the search parameter. The string parameter will be converted to a regular expression:

Example

Use a string to perform a search for "W3school":

var str = "Visit CodeW3C.com!";
var n = str.search("W3School");

Try It Yourself

Use regular expressions in the string method search()

Example

Perform a case-insensitive search for the string "codew3c" within the search string using regular expressions:

var str = "Visit CodeW3C.com";
var n = str.search(/codew3c/i);

The result of n will be:

6

Try It Yourself

Use the string method replace() to process strings

replace() Also accepts strings as search parameters:

var str = "Visit Microsoft!";
var res = str.replace("Microsoft", "W3School");

Try It Yourself

Use regular expressions in the string method replace()

Example

Use case-insensitive regular expressions to replace 'Microsoft' with 'W3school' in the string:

var str = "Visit Microsoft!";
var res = str.replace(/microsoft/i, "W3School");

The result of res will be:

Visit CodeW3C.com!

Try It Yourself

Did you notice?

Regular expression parameters (instead of string parameters) can be used in the above methods.

Regular expressions can make your search more powerful (for example, case-insensitive).

Regular expression modifier

ModifierCan be used for case-insensitive search at a more global level:

Modifier Description Try it
i Perform case-insensitive matching. Try it
g Perform global matching (find all matches instead of stopping after finding the first match). Try it
m Perform multiline matching. Try it

Regular expression pattern

ParenthesesUsed to find strings within a certain range:

Expression Description Try it
[abc] Find any character within square brackets. Try it
[0-9] Find any digit from 0 to 9. Try it
(x|y) Find any of the options separated by '|'. Try it

Metacharacter (Metacharacter)They are characters with special meanings:

Metacharacter Description Try it
\d Find digits. Try it
\s Find whitespace characters. Try it
\b Match word boundaries. Try it
\uxxxx Find Unicode characters specified by the hexadecimal number xxxx. Try it

Quantifiers Define quantifiers:

Quantifier Description Try it
n+ Match any string containing at least one 'n'. Try it
n* Match any string containing zero or more 'n's. Try it
n? Match any string containing zero or one 'n'. Try it

Use the RegExp object

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

Use test()

test() It is a regular expression method.

It searches for strings through patterns and then returns true or false based on the results.

The following example searches for the character 'e' in the string:

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 above code will be:

true

Try It Yourself

You do not need to put the regular expression into a variable first. The two lines above can be shortened to one line:

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

Using exec()

exec() A method is a regular expression method.

It searches the string through the specified pattern and returns the text found.

If no match is found, it returns null.

The following example searches for the character 'e' in the string:

Example

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

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

e

Try It Yourself

Complete RegExp Reference Manual

For a complete reference manual, please visit our full JavaScript RegExp Reference Manual.

This reference manual includes descriptions and examples of all RegExp properties and methods.