ddd-ts-kit/clean-no-magic-number

Architecture id: clean/no-magic-number. Default severity: error.

Applies to: domain/ and application/ of every context of a project whose config says "stack.literals": "named", which init writes (a config that does not say, as before 0.6, keeps the rule silent); tests excluded.

Why

hours * 60, limit = 100, padStart(2, '0'): a number in the middle of the model says neither what it is nor who decided it. The second copy of it drifts from the first, and a rule of the business (a booking window, a reminder delay, a page limit) hides in an expression. Named once, it reads as the language: MINUTES_PER_HOUR, LONGEST_ADDRESS, BookingWindow.standard().

Reported

A number or bigint literal, the minus included, that is not:

• 0, 1 or -1 (configurable);
• an index, items[2];
• a type, type Hour = 7 | 8, or the value of an enum member;
• in the initializer of a constant of the module (const MINUTES_PER_HOUR = 60;, an object or an array as const included) or of a static readonly field, with no function in between.

Incorrect:

function minuteOf(hours: number, minutes: number): number {
  return hours * 60 + minutes;
}

Correct:

const MINUTES_PER_HOUR = 60;

function minuteOf(hours: number, minutes: number): number {
  return hours * MINUTES_PER_HOUR + minutes;
}

Details

A duration, an amount, a limit or a rate of the business is better a value object than a constant (BookingWindow, Money): the constant names the number, the value object also carries its rules.

Options

allow: the numbers allowed anywhere, [0, 1, -1] by default.

'ddd-ts-kit/clean-no-magic-number': ['error', { allow: [0, 1, -1, 2] }]

rules."clean/no-magic-number" in ddd-ts-kit.config.json set to off silences the rule, and // ddd-ts-kit-disable-next-line clean/no-magic-number -- <reason> silences one line, exactly as for ddd-ts-kit check.

Limits

• A constant of a function body, const limit = 100 inside execute, is reported: it is named, but decided where it is used.
• Infrastructure, presentation and the platform are not judged: a port number or a page size of a route are configuration.

With the CLI checker

None: the rule needs a syntax tree. ddd-ts-kit check knows its id so that the config can set its severity.