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Table of Contents
Create regular expressions
Common matching operations
Common modifiers and metacharacters
Tips for practical application
Home Web Front-end JS Tutorial How to Use Regular Expressions (RegEx) in JavaScript

How to Use Regular Expressions (RegEx) in JavaScript

Jul 13, 2025 am 01:57 AM
regular expression

Regular expressions are used in JavaScript to process strings, providing two ways to create: literals such as /abc/ and constructor new RegExp('abc'); common methods include test() to check matches, match() to get result arrays, replace() to replace content; common modifiers include i (ignoring case), g (global search), metacharacters such as \d to match numbers, and . to match any character; application techniques include using online tools to test, escape special characters, and grouping data with brackets. Mastering basic syntax and methods can meet the needs of multi-digit string processing.

How to Use Regular Expressions (RegEx) in JavaScript

Regular expressions (RegEx) are powerful tools for handling strings, especially in JavaScript. If you need to do form verification, text extraction or replacement operations, mastering basic RegEx usage will save a lot of time.

How to Use Regular Expressions (RegEx) in JavaScript

Create regular expressions

JavaScript provides two ways to create regular expressions: literals and constructors.

  • Using slashes / is the most common way:

    How to Use Regular Expressions (RegEx) in JavaScript
     const regex = /abc/;
  • Use RegExp constructor more flexible and suitable for dynamically generated regularity:

     const pattern = 'abc';
    const regex = new RegExp(pattern);

The two functions are the same, the difference is that the constructor allows you to pass in variables, which is more suitable for runtime splicing rules.

How to Use Regular Expressions (RegEx) in JavaScript

Common matching operations

The real role of RegEx is in matching and processing strings. Several commonly used methods include:

  • test() : Check whether it matches and returns a boolean value.

     const regex = /hello/;
    regex.test('hello world'); // true
  • match() : used for strings, return a matching result array or null.

     'hello world'.match(/hello/); // ["hello", index: 0, input: "hello world", groups: undefined]
  • replace() : replaces the matching content.

     'hello world'.replace(/world/, 'there'); // "hello there"

These methods are the most used every day, and it is recommended to be familiar with their basic behavior, especially the return value format, to avoid errors.

Common modifiers and metacharacters

There are some common symbols in regular expressions that can enhance matching capabilities:

  • i : Ignore case
    /hello/i can match "HELLO" or "hello"

  • g : Global search
    /a/g will find all "a", instead of stopping the first one

  • \d matches numbers, \w matches letters, numbers or underscores, . matches any character (except for line breaks)

For example: If you want to extract all email addresses in a paragraph of text, you can write a regular like this:

 const text = 'Contact us at support@example.com or sales@company.org.';
const emails = text.match(/[a-zA-Z0-9._% -] @[a-zA-Z0-9.-] \.[az]{2,}/g);
// ["support@example.com", "sales@company.org"]

Although this rule looks a bit long, it has a clear structure and each part has a clear purpose.

Tips for practical application

  • Test regular expressions : You can use online tools like regex101.com to try while writing to reduce debugging time.
  • Escape special characters : If you want to match symbols like . or ? , these symbols that have meaning in themselves need to be escaped with a \ , such as /\.com/ to correctly match .com .
  • Grouping and Capture : Use brackets () to extract the matching content of a certain part of it separately, which is often used to parse data.

For example, extract the domain name from the URL:

 const url = 'https://example.com/path/to/page';
const match = url.match(/https?:\/\/([^\/] )/);
// match[1] is "example.com"

Basically that's it. Regularity cannot be mastered in one or two days, but as long as you master the basic grammar and common methods, you can handle most of the situations.

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