# no-control-regex

> Disallow control characters in regular expressions

The characters U+0000 to U+001F are invisible and rarely appear in text you want to match. When one shows up in a regular expression, it's often a typo in an escape, such as `\x0C` where you meant `\xC0`.

The rule reports a raw control character and the escapes `\x0A`, `\u000A` and, with the `u` or `v` flag, `\u{A}`. It checks regular expression literals and strings passed to `RegExp`. Named escapes such as `\t`, `\n` and `\cJ` are allowed.

This rule is on by default.

## Configure

On by default as a warning. To turn it off:

```toml bunfig.toml
[lint.rules]
"no-control-regex" = "off" # or "error"
```

## Examples

Reported:

```js
const lineBreak = /\x0A/;

const separator = new RegExp("\x1F");
```

Not reported:

```js
const lineBreak = /\n/;

const space = /\x20/;
```

In a string, `"\n"` is the raw character by the time `RegExp` sees it. Escape the backslash:

```js
const lineBreak = new RegExp("\n");
```

```js
const lineBreak = new RegExp("\\n");
```

## When not to use it

Some formats are built on control characters. Terminal color codes start with `\x1B`, so a pattern that strips them needs to contain it. Disable the rule for that line:

```js
// eslint-disable-next-line no-control-regex
const colorCodes = /\x1B\[[0-9;]*m/g;
```