有时候需要一个类型，是依赖于上一个类型但是，对属性的要求去不同interface Person{name: string;agent: number;
}
type Person2 = Readonly<Person>;
type Person3 = Partial<Person>;
class Test {run() {let person: Person = {name: 'dd',agent: 1};person.name = 'cc';let person2: Person2 = {name: 'read',agent: 1};// person2.agent = 3; 报错let person3: Person3 = {name: 'person 3' // 属性不完整也不会报错}}
}ReadOnly、Partial源码type Readonly<T> = {readonly [P in keyof T]: T[P];
}
type Partial<T> = {[P in keyof T]?: T[P];
}用 in， keyof即可实现type Pick<T, K extends keyof T> = {[P in K]: T[P];
}
type Record<K extends string, T> = {[P in K]: T;
}
)
