Lesson 66 - Grouping & Capturing in Regular Expressions

Regular expressions allow us to group parts of a pattern using parentheses (...). This is useful when we need to capture specific parts of a string for further processing.

Grouping in Regular Expressions

Grouping is mainly used for repeating multiple characters together and capturing substrings.

Example 1: Using Groups for Repetition

let regex = /(ha)+/;
console.log("hahaha".match(regex)); // Output: ["hahaha"]

Here, (ha)+ means "repeat the ha sequence at least once."

Capturing Groups

Capturing groups store the matched parts so you can access them later.

Example 2: Extracting Parts of a String

let regex = /My name is (\w+)/;
let result = "My name is John".match(regex);

console.log(result[1]); // Output: "John"

The parentheses capture the name, allowing us to extract "John" from the string.

Non-Capturing Groups

If you don’t want to store the match, use (?:...).

let regex = /(?:ha)+/;
console.log("hahaha".match(regex)); // Output: ["hahaha"]

Unlike regular groups, this does not store "ha" separately.

Using Groups with replace()

Captured groups are useful when modifying text.

let regex = /(\w+)@(\w+).com/;
let str = "Email: test@example.com";
let replaced = str.replace(regex, "[$1 at $2]");

console.log(replaced); // Output: "Email: [test at example]"

Try Your Hand ?

1. Write a regex to match a date format like 12-05-2025 and extract day, month, and year.
2. Modify a string like "Hello John, meet Sarah" to "Hello, John! Meet, Sarah!" using regex groups.