JavaScript RegExp ? Quantifier

What Is ??

The ? quantifier means zero or one of the previous token. It makes that token optional: present once, or missing. Classic uses include https? (http or https) and -?\d+ (optional minus before digits).

token?     → zero or one of token  (same as {0,1})

/https?/  on "http"   → "http"
/https?/  on "https"  → "https"
/colou?r/ on "color"  → "color"
/colou?r/ on "colour" → "colour"

not the same as (?=...) lookahead — context matters

How to Use ?

Place ? right after the token you want to make optional.

1. Choose the token: a character, class, or group.
2. Add ? immediately after it (e.g. s? or (Mr\. )?).
3. Remember: at most one match — for many repeats use * or +.
4. Do not confuse with (?=...) — that ? starts a lookahead, not optional matching.

Pseudocode

re = /token?/

if next text matches "token":
    take it once (greedy prefers yes)
else:
    take nothing — still OK

never take "token" more than once

Cheat Sheet

Keep these ? facts handy.

Live Preview

Run common ? patterns and see what matches.

/https?/.exec("http")
→ "http"

/* s? is optional — zero s is fine */

JavaScript Examples

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

const schemes = ["http", "https", "ftp"];

for (const s of schemes) {
  console.log(s, s.match(/https?/));
}
// http  ["http"]
// https ["https"]
// ftp   null

http [ 'http', index: 0, input: 'http', groups: undefined ]
https [ 'https', index: 0, input: 'https', groups: undefined ]
ftp null

const words = ["color", "colour", "colar"];

for (const w of words) {
  console.log(w, /colou?r/.test(w));
}
// color  true
// colour true
// colar  false

color true
colour true
colar false

const text = "scores: 12, -3, and 0";

console.log(text.match(/-?\d+/g));
// ["12", "-3", "0"]

[ '12', '-3', '0' ]

Performance Notes

A single ? is cheap. Nested optional groups on long strings can create extra backtracking paths—prefer clear, short patterns for beginners and production alike.

Key Takeaways