unicorn/numeric-separators-style Style

What it does

Enforces a convention of grouping digits using numeric separators.

Why is this bad?

Long numbers can become really hard to read, so cutting it into groups of digits, separated with a _, is important to keep your code clear. This rule also enforces a proper usage of the numeric separator, by checking if the groups of digits are of the correct size.

Examples

Examples of incorrect code for this rule:

const invalid = [1_23_4444, 1_234.56789, 0xab_c_d_ef, 0b10_00_1111, 0o1_0_44_21, 1_294_28771_2n];

Examples of correct code for this rule:

const valid = [1_234_567, 1_234.567_89, 0xab_cd_ef, 0b1000_1111, 0o10_4421, 1_294_287_712n];

Configuration

This rule accepts a configuration object with the following properties:

binary

type: object

Configuration for binary literals (e.g. 0b1010_0001 and bigint variants). Controls how digits are grouped and when separators are applied.

binary.groupLength

type: integer

The number of digits per group when inserting numeric separators. For example, a groupLength of 3 formats 1234567 as 1_234_567.

binary.minimumDigits

type: integer

The minimum number of digits required before grouping is applied. Values with fewer digits than this threshold will not be grouped.

hexadecimal

type: object

Configuration for hexadecimal literals (e.g. 0xAB_CD, 0Xab_cd, and bigint variants). Controls how digits are grouped and when separators are applied.

hexadecimal.groupLength

type: integer

The number of digits per group when inserting numeric separators. For example, a groupLength of 3 formats 1234567 as 1_234_567.

hexadecimal.minimumDigits

type: integer

The minimum number of digits required before grouping is applied. Values with fewer digits than this threshold will not be grouped.

number

type: object

Configuration for decimal numbers (integers, fraction parts, and exponents). Controls how digits are grouped and when separators are applied.

number.groupLength

type: integer

The number of digits per group when inserting numeric separators. For example, a groupLength of 3 formats 1234567 as 1_234_567.

number.minimumDigits

type: integer

The minimum number of digits required before grouping is applied. Values with fewer digits than this threshold will not be grouped.

octal

type: object

Configuration for octal literals (e.g. 0o1234_5670 and bigint variants). Controls how digits are grouped and when separators are applied.

octal.groupLength

type: integer

The number of digits per group when inserting numeric separators. For example, a groupLength of 3 formats 1234567 as 1_234_567.

octal.minimumDigits

type: integer

The minimum number of digits required before grouping is applied. Values with fewer digits than this threshold will not be grouped.

onlyIfContainsSeparator

type: boolean

default: false

Only enforce the rule when the numeric literal already contains a separator (_).

When true, numbers without separators are left as-is; when false (default), grouping will be enforced for eligible numbers even if they don't include separators yet.

How to use

To enable this rule using the config file or in the CLI, you can use:

Config (.oxlintrc.json)

{
  "rules": {
    "unicorn/numeric-separators-style": "error"
  }
}

CLI

oxlint --deny unicorn/numeric-separators-style

References

• Rule Source