![JavaScript RegExp [abc] character class — match one character from a set](/images/group-abc.webp)
[abc]?[abc] is a character class that matches one character from a custom set — here a, b, or c. Order inside the brackets does not matter.
/[abc]/ → one of: a, b, or c
/[abc]+/ → one or more from that set
/[abc]/i → case-insensitive (also A, B, C)
[abc] ≠ (abc)
set of one char vs literal "abc"| Use | Prefer |
|---|---|
| One of a few letters | /[abc]/ |
| Any lowercase letter | /[a-z]/ (range) |
| Not those letters | /[^abc]/ |
[abc]List the allowed characters inside [ ], then test or extract.
[abc].+, {n}) if you need more than one match in a row.test() for yes/no, or exec() / match() to read the character."abc" — use (abc) for that sequence.| Piece | Required? | Role |
|---|---|---|
[abc] | Yes | Matches one character from the set |
| Quantifier | Optional | +, {2}, etc. for length |
i flag | Optional | Ignore case for the letters |
pattern = /[abc]/ // or /[abc]+/, /[abc]/i
str = text to check
if pattern.test(str):
// at least one of a, b, c found
match = pattern.exec(str)
// match[0] is the character (or run)Keep these patterns handy while matching a small set of characters.
| Pattern | Matches |
|---|---|
/[abc]/ | One of a, b, c |
/[abc]+/ | One or more from that set |
/[abc]/i | Also A, B, C |
/^[abc]$/ | Whole string is one of those letters |
/[a-z]/ | Any lowercase letter (range) |
/[^abc]/ | One character that is not a, b, or c |
Pick a sample string and see whether /[abc]/ finds a match.
Short, copy-ready snippets. Open DevTools Console, or use Try It Yourself for a live editor.
Use test() and exec() with /[abc]/.
const set = /[abc]/;
console.log(set.test("cab")); // true
console.log(set.test("dog")); // false
console.log(set.exec("xby")[0]); // "b"/[abc]/ matches one of a, b, or c."cab" starts with c → true."dog" has none of those letters → false.exec("xby") returns the first match "b".Add + to grab a run of allowed letters.
const run = /[abc]+/g;
const str = "ab and cab";
console.log(str.match(run));
// ["ab", "cab"][abc]+ means one or more letters from the set in a row.g finds every run in the string.["ab", "cab"].Use the i flag so uppercase letters count too.
const set = /[abc]/i;
console.log(set.test("Apple")); // true (A)
console.log(set.test("dog")); // false
console.log(set.exec("XB")[0]); // "B"i, A would not match [abc]./[abc]/i also accepts A, B, and C.A matches → true.Check these before treating [abc] like a word match.
[abc] matches one letter. (abc) matches the literal word "abc".
A does not match [abc] unless you add i or list A in the brackets.
Use + or {n} when you need a run of letters from the set.
[^abc] is the oppositeA leading ^ inside brackets means “not these.” See [^abc].
Character classes like [abc] are a core part of JavaScript regular expressions — available in every environment.
Supported in all browsers and Node.js versions since early ECMAScript. No polyfill needed.
Bottom line: Use freely. List only the characters you need; use ranges like [a-z] when the set is large.
| Approach | Cost | Best for |
|---|---|---|
/[abc]/ | O(n) scan | Detect any set letter |
/[abc]+/g | O(n) scan | Extract runs from the set |
/^[abc]$/ | O(1)–O(n) | Single-letter codes |
Small character classes are cheap. Prefer a clear set ([abc]) over listing alternations like a|b|c when matching one character.
[abc] matches one character from a custom set.(abc) for the literal sequence "abc".+ or {n} for runs from the set.i or list both cases.One line: [abc] means “one of these characters” — not the word abc.
Learn the negated digit class — match anything that is not a digit.
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