Quantifiers, greediness and explicit delimiters

Understand the mechanism

* means zero or more, + one or more, ? zero or one, and {m,n} bounds repetition. A quantifier applies to the immediately preceding atom or group, not the entire pattern.

Greedy quantifiers first try more characters; a following ? makes a quantifier lazy, initially trying fewer. Both are constrained by the remaining pattern. Lazy does not mean no backtracking or automatically faster.

For content that cannot contain a closing bracket, an explicit negated class expresses the boundary more directly than .*. This exercise handles flat labels, not nested brackets or HTML.

Runnable example

const text = "[one] [two]";
console.log(JSON.stringify(text.match(/\[.*\]/g)));
console.log(JSON.stringify(text.match(/\[.*?\]/g)));
console.log(JSON.stringify(text.match(/\[[^\]\r\n]+\]/g)));
console.log(JSON.stringify(["", "a", "aaaa"].map(s => /^a{1,3}$/.test(s))));

Trace and verify

The greedy pattern spans from the first opening bracket to the final closing bracket. The other patterns return separate one and two labels. Repetition 1 to 3 rejects both empty input and four a characters.

Common mistakes and boundaries

.*? can still match empty content. Decide explicitly whether [] is valid, and whether a negated class should permit newlines.

Practice challenge

Modify the third pattern to allow an empty [] label.

Reference solution and reasoning

Replace + after the negated class with *. Both [] and [one] match, while line breaks remain excluded.

Further reading

• MDN regular expressions