no-empty-character-class

Disallow empty character classes in regular expressions

✅

Using the recommended config from @eslint/js in a configuration file enables this rule

Because empty character classes in regular expressions do not match anything, they might be typing mistakes.

const foo = /^abc[]/; 1

Rule Details

This rule disallows empty character classes in regular expressions.

Examples of incorrect code for this rule:

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/*eslint no-empty-character-class: "error"*/ /^abc[]/.test("abcdefg"); // false "abcdefg".match(/^abc[]/); // null /^abc[[]]/v.test("abcdefg"); // false "abcdefg".match(/^abc[[]]/v); // null /^abc[[]--[x]]/v.test("abcdefg"); // false "abcdefg".match(/^abc[[]--[x]]/v); // null /^abc[[d]&&[]]/v.test("abcdefg"); // false "abcdefg".match(/^abc[[d]&&[]]/v); // null const regex = /^abc[d[]]/v; regex.test("abcdefg"); // true, the nested `[]` has no effect "abcdefg".match(regex); // ["abcd"] regex.test("abcefg"); // false, the nested `[]` has no effect "abcefg".match(regex); // null regex.test("abc"); // false, the nested `[]` has no effect "abc".match(regex); // null 1
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Examples of correct code for this rule:

Open in Playground

/*eslint no-empty-character-class: "error"*/ /^abc/.test("abcdefg"); // true "abcdefg".match(/^abc/); // ["abc"] /^abc[a-z]/.test("abcdefg"); // true "abcdefg".match(/^abc[a-z]/); // ["abcd"] /^abc[^]/.test("abcdefg"); // true "abcdefg".match(/^abc[^]/); // ["abcd"] 1
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Known Limitations

This rule does not report empty character classes in the string argument of calls to the RegExp constructor.

Example of a false negative when this rule reports correct code:

/*eslint no-empty-character-class: "error"*/ const abcNeverMatches = new RegExp("^abc[]"); 1
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Version

This rule was introduced in ESLint v0.22.0.

Resources

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