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What is regex in JavaScript

Understanding Regular Expressions (Regex)

When you first encounter regular expressions, commonly known as regex, it might seem like an indecipherable code language. But don't worry, by the end of this blog, you will have a solid understanding of what it is and how to use it in JavaScript.

What is Regex?

In simple terms, a regular expression is a sequence of characters that forms a search pattern. The pattern can be used to match, locate, and manage text. It's like a sophisticated "find and replace" function in a word processor, but for your code.

The Basics of Regex in JavaScript

In JavaScript, a regex can be created in two ways. The first way is by using the RegExp constructor:

let regex1 = new RegExp('abc');

The second way is by using a regular expression literal, which consists of a pattern enclosed between slashes:

let regex2 = /abc/;

Both of these examples illustrate a regex that matches the string "abc".

Regex Methods in JavaScript

There are primarily two methods in JavaScript that deal with regular expressions:

  • test()
  • exec()

The test() method takes the regex and applies it to a string (which is provided as an input) and returns true if the pattern is found in the string. If not, it returns false.

let regex = /abc/;
console.log(regex.test('abcdef')); // Output: true
console.log(regex.test('abdef'));  // Output: false

The exec() method is a bit more complex. It also takes a string as an input and returns an array containing all matched groups if the pattern is found. If the pattern is not found, it will return null.

let regex = /a(b)c/;
console.log(regex.exec('abcdef')); // Output: [ 'abc', 'b', index: 0, input: 'abcdef', groups: undefined ]

Here, 'b' is a matched group in the pattern 'abc'.

Special Characters in Regex

Regex uses certain special characters to enable more complex and versatile matching options. Here are a few examples:

. (Dot): This special character matches any single character except for newline characters. For example, /.n/ would match 'an' and 'on' in "And on it goes".

* (Asterisk): This special character matches the preceding character 0 or more times. For example, /a*/ would match 'a', 'aa', 'aaa' in "aaabc".

+ (Plus): This special character matches the preceding character 1 or more times. For example, /a+/ would match 'a', 'aa', 'aaa' in "aaabc".

? (Question mark): This special character makes the preceding character optional. For example, /ea?/ would match 'e' and 'ea' in "least".


Think of regex as the Swiss Army Knife of text processing. It's incredibly powerful and can make your tasks much easier once you get the hang of it. However, with great power comes great responsibility. Regex can be difficult to read and understand if overused or misused, so it's often a good idea to comment your regex or break it down into smaller, more manageable pieces.

Just like a new language, regular expressions take time to learn and master. But don't be discouraged. The more you use them, the more they'll make sense. And soon, you'll be wielding regex like a pro, using them to solve complex text processing problems with ease.

Remember, coding is a journey of constant learning. Keep exploring, keep experimenting, and most importantly, have fun along the way. Happy coding!