nonOctalDecimalEscapes

Reports non-octal decimal escape sequences (\8 and \9) in string literals.

✅ This rule is included in the ts logical preset.

The escape sequences \8 and \9 in string literals are legacy features that behave as identity escapes, meaning they simply represent the literal digits “8” and “9”. While these were allowed in most JavaScript engines before ECMAScript 2021, they are now specified as non-octal decimal escape sequences and are considered optional in the specification. These escape sequences are not supported in strict mode in all environments and should be avoided when writing new code.

Examples

❌ Incorrect

const value = "\8";

const message = "w\8less";

const date = "December 1\9";

const text = "Don't use \8 and \9 escapes.";

✅ Correct

const value = "8";

const message = "w8less";

const date = "December 19";

const text = "Don't use \\8 and \\9 escapes.";

Options

This rule is not configurable.

When Not To Use It

If your project has portions that perform raw string manipulations and rely on legacy octal escape sequences, it might be difficult to refactor towards code that passes this rule. You might consider using Flint disable comments and/or configuration file disables for those specific situations instead of completely disabling this rule.

Further Reading

• MDN: Escape sequences
• ECMAScript® Specification: Non-octal decimal escape sequences

Equivalents in Other Linters

• Biome: noNonoctalDecimalEscape
• ESLint: no-nonoctal-decimal-escape
• Oxlint: eslint/no-nonoctal-decimal-escape