Because empty character classes in regular expressions do not match anything, they might be typing mistakes.
js
const foo = /^abc[]/;Rule Details ​
This rule disallows empty character classes in regular expressions.
Examples of incorrect code for this rule:
::: incorrect
js
/*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:::
Examples of correct code for this rule:
::: correct
js
/*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"]:::
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:
js
/*eslint no-empty-character-class: "error"*/
const abcNeverMatches = new RegExp("^abc[]");