# TS1499: Unknown regular expression flag.

> A regular expression literal has a flag that doesn't exist. Use only `d`, `g`, `i`, `m`, `s`, `u`, `v` and `y`.

## What it means

The letters after the closing `/` of a regular expression are its flags. Only `d`, `g`,
`i`, `m`, `s`, `u`, `v` and `y` exist; any other letter is reported.

## Example

```ts
export const re = /abc/x;
```

## How to fix

- Remove the unknown flag. JavaScript has no `x` (extended) flag; write the pattern without
  whitespace and comments.

Source: https://ts-r.dev/errors/TS1499/