Working with Regular Expressions in JavaScript
Jul 07, 2025 am 12:36 AMThe key to handling regular expressions in JavaScript is to master basic syntax and common usage. 1. There are two ways to create: literals (/pattern/flags) are suitable for fixed content, and constructors (new RegExp()) are suitable for dynamic generation; 2. Common modifiers include g (global matching), i (ignoring case), and m (multi-line pattern); 3. Basic operations include test() (detecting match), match() (extracting match), replace() (replace content), and split() (split string); 4. When replacing, you can use $1 and $2 references to group, or use functions to dynamically process. By mastering these core points, you can meet the regular needs of daily development.
It is actually not that difficult to deal with regular expressions in JavaScript. The key is to understand the basic grammar and common usage, and then flexibly use it in combination with actual scenarios.

How to create regular expressions
There are two ways to create regular expressions in JavaScript: literals and constructors .
Using literals is simpler and more intuitive, such as /pattern/flags
, while the constructor is new RegExp('pattern', 'flags')
.
When to use which one? If your regular content is fixed, it is recommended to use literals; if you need to dynamically generate regular expressions (such as user input), you have to use constructors.

For example:
- Fixed matching email:
/\S @\S \.\S /
- Dynamic replacement keywords:
new RegExp(searchTerm, 'g')
Common modifiers and uses
Modifiers affect matching behavior, and there are three common ones:

-
g
: Global match, find all results instead of stopping if you find the first one -
i
: Ignore case, for example,/hello/i
can match "HELLO", "hello", etc. -
m
: Multi-line pattern, let^
and$
match the beginning and end of each row respectively
For example, if you want to find all the "error" in a piece of text, regardless of upper and lower case, you can write it as: /error/gi
For example, if you want to determine whether a string starts with a certain word, but may have multiple lines of content, you need to add an m
modifier.
Basic operations of matching and extraction
JavaScript provides several common methods to operate regular operations:
-
test()
: Check whether it matches, returns a boolean value, suitable for conditional judgment -
match()
: Find matches in a string, return an array or null -
replace()
: replaces matching content, often used to clean or format data -
split()
: split strings according to regular intervals, such as splitting by multiple spaces
For example, verify whether the mobile phone number meets the format:
/^\d{11}$/.test('13800138000') // true
Extract all links from a paragraph:
str.match(/https?:\/\/[^\s] /g)
Tips for substitution and grouping
If you want to use matching content during replacement, you can use $1
and $2
to reference the grouping.
For example, change the date format from YYYY-MM-DD
to DD/MM/YYYY
:
'2025-04-05'.replace(/(\d{4})-(\d{2})-(\d{2})/, '$3/$2/$1')
Parentheses are used here to define the capture group, and then the corresponding part is referenced by numbers in the replacement string.
Another situation is dynamic processing of the replacement function, such as capitalizing the first letter of each matching word:
str.replace(/\b\w /g, word => word.charAt(0).toUpperCase() word.slice(1))
Basically that's it. It’s almost time to master these points and cope with the regular needs in daily development.
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