JavaScript RegExp g Flag

What Is the g Flag?

The g flag (global) tells the regex engine to find every match in a string—not stop after the first hit. It powers replace-all, matchAll(), and exec() loops that walk through all occurrences.

/pattern/g          // enable global
regex.global        // true when g is set
regex.lastIndex     // search cursor (advances with g)

match()  + g  → all matched strings
replace() + g → replace every match
exec()   + g  → next match each call

How to Use the g Flag

Add g, then choose the method that fits your goal.

1. Create a global regex: /pattern/g or new RegExp("pattern", "g").
2. Use match for a simple list of strings, or replace to change every hit.
3. Use matchAll or an exec loop when you need capture groups / index for each match.
4. Before reusing the same global regex on a fresh scan, set re.lastIndex = 0.

Pseudocode

re = /pattern/g
re.lastIndex = 0

loop:
    m = re.exec(text)
    if m is null:
        stop
    else:
        use m[0], m.index, groups…
        // lastIndex already moved past this match

Cheat Sheet

Keep these global-flag facts handy.

Live Preview

Compare global vs non-global behavior on "cat dog cat bird cat".

text.match(/cat/g)
→ ["cat", "cat", "cat"]

/* g finds every "cat" */

JavaScript Examples

Short, copy-ready snippets. Open DevTools Console, or use Try It Yourself for a live editor.

const text = "cat dog cat bird cat";

console.log(text.match(/cat/g));  // ["cat", "cat", "cat"]
console.log(text.match(/cat/));   // ["cat", index: 0, …]

console.log(/cat/g.global);       // true
console.log(/cat/.global);        // false

[ 'cat', 'cat', 'cat' ]
[ 'cat', index: 0, input: 'cat dog cat bird cat', groups: undefined ]
true
false

const text = "cat cat cat";

console.log(text.replace(/cat/g, "pet"));  // "pet pet pet"
console.log(text.replace(/cat/, "pet"));   // "pet cat cat"

pet pet pet
pet cat cat

const re = /\d+/g;
const text = "a1 b22 c333";
const found = [];
let m;

while ((m = re.exec(text)) !== null) {
  found.push(m[0]);
}

console.log(found);         // ["1", "22", "333"]
console.log(re.lastIndex);  // 11

[ '1', '22', '333' ]
11

Performance Notes

Global search still walks the string once. Prefer match for plain strings; use matchAll or exec when you need capture details. Avoid restarting from scratch for each hit.

Key Takeaways