structural-typing

TypeScript uses structural typing: if it has the right shape, it fits.

Unlike nominal typing (where types must be explicitly declared), TypeScript checks structure. Understanding this prevents surprises and unlocks powerful patterns.

If you're surprised that TypeScript accepts a value, you're probably assuming nominal typing.

當對 TypeScript 接受意外值感到驚訝時使用。設計函數參數時使用。使用模擬物件進行測試時使用。 來源：marius-townhouse/effective-typescript-skills。