unicorn/numeric-separators-style Style
What it does
Enforces a convention of grouping digits using numeric separators.
Why is this bad?
A long series of digits can be difficult to read, and it can be difficult to determine the value of the number at a glance. Breaking up the digits with numeric separators (_) can greatly improve readability.
Compare the following two numbers and how easy it is to understand their magnitude:
1000000000;
1_000_000_000;This rule also enforces proper group size, for example enforcing that the _ separator is used every 3 digits.
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:
{
"rules": {
"unicorn/numeric-separators-style": "error"
}
}oxlint --deny unicorn/numeric-separators-style