How to Use Global Flag in Regex JavaScript: Simple Guide

In JavaScript, add the g flag to a regular expression to search for all matches in a string instead of stopping at the first match. For example, /pattern/g enables global matching, allowing methods like match() or replace() to work on every occurrence.

Syntax

The global flag g is added after the closing slash of a regular expression to enable searching for all matches in a string.

• /pattern/g: The pattern is the text or pattern you want to find.
• g: The global flag tells JavaScript to find all matches, not just the first.

javascript

/pattern/g

Example

This example shows how the global flag finds all occurrences of the word "cat" in a string.

javascript

const text = "cat bat cat rat cat";
const regexWithoutG = /cat/;
const regexWithG = /cat/g;

const firstMatch = text.match(regexWithoutG);
const allMatches = text.match(regexWithG);

console.log("First match without global flag:", firstMatch);
console.log("All matches with global flag:", allMatches);

Output

First match without global flag: [ 'cat', index: 0, input: 'cat bat cat rat cat', groups: undefined ]
All matches with global flag: [ 'cat', 'cat', 'cat' ]

Common Pitfalls

Without the global flag, regex methods like match() return only the first match. Forgetting g can cause unexpected results when you want all matches.

Also, when using the global flag with exec(), the regex object keeps track of the last index, so repeated calls find successive matches.

javascript

const text = "dog dog dog";
const regex = /dog/g;

console.log(regex.exec(text)); // First match
console.log(regex.exec(text)); // Second match
console.log(regex.exec(text)); // Third match
console.log(regex.exec(text)); // null (no more matches)

Output

[ 'dog', index: 0, input: 'dog dog dog', groups: undefined ]
[ 'dog', index: 4, input: 'dog dog dog', groups: undefined ]
[ 'dog', index: 8, input: 'dog dog dog', groups: undefined ]
null

Quick Reference

Flag	Meaning	Effect
g	Global	Find all matches, not just the first
i	Ignore case	Match letters regardless of case
m	Multiline	Make ^ and $ match start/end of lines

Key Takeaways

Add the 'g' flag to regex to find all matches in a string.

Without 'g', methods like match() return only the first match.

Using 'g' with exec() lets you find matches one by one.

Remember to reset regex lastIndex or create a new regex when reusing with 'g'.

Combine 'g' with other flags like 'i' for case-insensitive global search.