unicorn/numeric-separators-style

1000000 and 10000000 are hard to tell apart. 1_000_000 is easy to read, but only if the groups are all the same size. 10_00_000 is worse than no separators.

By default, decimal numbers of five digits or more are grouped by three, hexadecimal numbers by two, and binary and octal numbers by four. Groups are counted from the right.

--fix rewrites the number.

Configure#

Off by default. To turn it on:

bunfig.toml

[lint.rules]
"unicorn/numeric-separators-style" = "error" # or "warn"

Every option, set to its default:

bunfig.toml

[lint.rules]
"unicorn/numeric-separators-style" = ["error", {
  onlyIfContainsSeparator = false,
  number = { minimumDigits = 5, groupLength = 3 },
  hexadecimal = { minimumDigits = 0, groupLength = 2 },
  binary = { minimumDigits = 0, groupLength = 4 },
  octal = { minimumDigits = 0, groupLength = 4 },
}]

Examples#

example.js4 problems

const population = 1000000;
const price = 12_34_567;
const color = 0xFF8800;
const flags = 0b10101010;

example.jsNo problems

const population = 1_000_000;
const price = 1_234_567;
const color = 0xFF_88_00;
const flags = 0b1010_1010;
const year = 2026;

Options#

Option	Default	What it does
`onlyIfContainsSeparator`	`false`	Only check numbers that already have a `_`.
`number`	`{ "minimumDigits": 5, "groupLength": 3 }`	Settings for decimal numbers.
`hexadecimal`	`{ "minimumDigits": 0, "groupLength": 2 }`	Settings for `0x` numbers.
`binary`	`{ "minimumDigits": 0, "groupLength": 4 }`	Settings for `0b` numbers.
`octal`	`{ "minimumDigits": 0, "groupLength": 4 }`	Settings for `0o` numbers.

Each of the four kinds takes these settings:

Setting	What it does
`groupLength`	How many digits are in a group.
`minimumDigits`	Numbers with fewer digits have no separators.
`onlyIfContainsSeparator`	Overrides the top-level option for this kind of number.
`fractionGroupLength`	Only for `number`. How many digits are in a group after the decimal point, counted from the left. By default the fraction has no separators.

With onlyIfContainsSeparator, a number without separators is left alone, and one with separators must have them in the right places:

example.jswith { "onlyIfContainsSeparator": true }No problems

const population = 1000000;

example.jswith { "onlyIfContainsSeparator": true }1 problem

const population = 10_00000;

To leave hexadecimal numbers such as colors alone unless they have a separator:

example.jswith { "hexadecimal": { "onlyIfContainsSeparator": true } }No problems

const color = 0xFF8800;

With minimumDigits, shorter numbers must not have separators:

example.jswith { "number": { "minimumDigits": 7 } }No problems

const timeout = 30000;
const population = 1_000_000;

example.jswith { "number": { "minimumDigits": 7 } }1 problem

const timeout = 30_000;

With fractionGroupLength:

example.jswith { "number": { "fractionGroupLength": 3 } }1 problem

const pi = 3.14159265;

example.jswith { "number": { "fractionGroupLength": 3 } }No problems

const pi = 3.141_592_65;