typescript高级类型看不懂系列一

type Type<T> = {[K in keyof T]:T[K] extends Function?K:never}**[keyof T]** interface Part { id: number; name: string; sub: Part[]; undatePart(name: string): void } type Test = Type<Part>

加粗的[keyof T]是啥意思呢？？？