[pve-eslint.git] / eslint / docs / rules / no-empty-character-class.md

# disallow empty character classes in regular expressions (no-empty-character-class)

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

```js
var foo = /^abc[]/;
```

## Rule Details

This rule disallows empty character classes in regular expressions.

Examples of **incorrect** code for this rule:

```js
/*eslint no-empty-character-class: "error"*/

/^abc[]/.test("abcdefg"); // false
"abcdefg".match(/^abc[]/); // null
```

Examples of **correct** code for this rule:

```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"]
```

## 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"*/

var abcNeverMatches = new RegExp("^abc[]");
```
Commit	Line	Data
eb39fafa DC	1	# disallow empty character classes in regular expressions (no-empty-character-class)
	2
	3	Because empty character classes in regular expressions do not match anything, they might be typing mistakes.
	4
	5	```js
	6	var foo = /^abc[]/;
	7	```
	8
	9	## Rule Details
	10
	11	This rule disallows empty character classes in regular expressions.
	12
	13	Examples of incorrect code for this rule:
	14
	15	```js
	16	/eslint no-empty-character-class: "error"/
	17
	18	/^abc[]/.test("abcdefg"); // false
	19	"abcdefg".match(/^abc[]/); // null
	20	```
	21
	22	Examples of correct code for this rule:
	23
	24	```js
	25	/eslint no-empty-character-class: "error"/
	26
	27	/^abc/.test("abcdefg"); // true
	28	"abcdefg".match(/^abc/); // ["abc"]
	29
	30	/^abc[a-z]/.test("abcdefg"); // true
	31	"abcdefg".match(/^abc[a-z]/); // ["abcd"]
	32	```
	33
	34	## Known Limitations
	35
	36	This rule does not report empty character classes in the string argument of calls to the `RegExp` constructor.
	37
	38	Example of a false negative when this rule reports correct code:
	39
	40	```js
	41	/eslint no-empty-character-class: "error"/
	42
	43	var abcNeverMatches = new RegExp("^abc[]");
	44	```