numericSeparatorGroups

Reports numeric literals with inconsistent separator grouping.

✅ This rule is included in the ts stylisticStrict presets.

This rule enforces consistent grouping of digits using numeric separators.

Numeric separators (_) make large numbers more readable by grouping digits. This rule enforces:

• Groups of 3 for decimal numbers (e.g., 1_000_000)
• Groups of 4 for binary and octal numbers (e.g., 0b1111_0000)
• Groups of 2 for hexadecimal numbers (e.g., 0xFF_FF)

Numbers with fewer than 5 digits are not required to use separators.

Examples

❌ Incorrect

const value = 1000000;

const value = 100_00;

const value = 0xffff;

const value = 0b11111111;

const value = 10000n;

✅ Correct

const value = 1_000_000;

const value = 10_000;

const value = 0xff_ff;

const value = 0b1111_1111;

const value = 10_000n;

const value = 1000;

Options

This rule is not configurable.

When Not To Use It

If you prefer not to use numeric separators, or have a codebase with a different convention for digit grouping, you may want to disable this rule.

Further Reading

• MDN: Numeric separators
• MDN: BigInt

Equivalents in Other Linters

• Biome: useNumericSeparators
• ESLint: unicorn/numeric-separators-style
• Oxlint: unicorn/numeric-separators-style