regexStandaloneBackslashes

Reports standalone backslashes in regex patterns that look like incomplete escape sequences.

✅ This rule is included in the ts logical and logicalStrict presets.

In non-unicode mode, backslashes followed by certain characters are interpreted as literal backslash characters rather than escape sequences.

For example, /\c/ (without the unicode flag) is equivalent to /\\c/ — a literal backslash followed by c. This behavior is described in Annex B of the ECMAScript specification.

Reports standalone backslashes (\) in regex patterns that don’t form a valid escape sequence.

Examples

Incomplete Control Escape

The \c escape requires a letter A-Z to form a valid control escape sequence.

❌ Incorrect

const pattern = /\c/;

✅ Correct

const pattern = /\cX/;

Invalid Control Escape Character

Using \c with a non-letter character results in a standalone backslash.

❌ Incorrect

const pattern = /\c1/;

✅ Correct

const pattern = /\cA/;

Inside Character Class

Standalone backslashes can also occur inside character classes.

❌ Incorrect

const pattern = /[\c]/;

✅ Correct

const pattern = /[\cA]/;

RegExp Constructor

The rule also checks regex patterns in RegExp constructor calls.

❌ Incorrect

const pattern = new RegExp("\\c");

✅ Correct

const pattern = new RegExp("\\cX");

Valid Escape Sequences

Standard escape sequences like \n, \t, \d, and \\ are valid and not reported.

✅ Correct

const whitespace = /\n\t\r/;
const digits = /\d+/;
const literalBackslash = /\\/;

Options

This rule is not configurable.

When Not To Use It

If your codebase intentionally uses standalone backslashes in regex patterns and you understand the Annex B behavior, you might prefer to disable this rule.

Further Reading

• MDN: Character escape
• ECMAScript Annex B: Regular Expressions Patterns

Equivalents in Other Linters

• ESLint: regexp/no-standalone-backslash