no-magic-numbers

No magic numbers

Do not leave unexplained numeric literals in behavior code. Name values that encode domain meaning, UI layout, input protocols, timing, or rendering.

Prefer

const MIDDLE_MOUSE_BUTTON = 1;
const VIEWPORT_SCALE_STEP = 0.1;
const DEFAULT_FONT_SIZE = 24;

if (event.button === MIDDLE_MOUSE_BUTTON) { /* … */ }

Colocate constants with the module that owns them, or share via a small *-constants.ts / existing domain module when reused across files.

Allowed without naming

• Loop / array indices and obvious arithmetic (i + 1, length - 1, / 2 for midpoint).
• Identity math (* 1, + 0) and empty defaults (0, 1 for scale/alpha when they are literal identities).
• Enum-like discriminants already expressed as string unions or typed enums.
• Test expectations that mirror a fixture’s explicit setup values in the same test.
• CSS in stylesheets / style objects when the number is a one-off layout token next to related styles (prefer design tokens when the value repeats).

Do not

• Scatter the same literal (e.g. 0.1, 24, button 1) across files — extract one shared constant.
• Name every trivial 0/1; name values a reader would otherwise have to reverse-engineer.
• Put renderer/UI literals into serialized scene defaults unless they are real domain defaults (then name them in the domain/factory module).