以 Person 為例
interface Person {
name: string;
age?: number;
}
Partial
源碼：
type Partial<T> = {
[P in keyof T]?: T[P];
};
實例：
type Person2 = Partial<Person>;
// Person2 === {name?: string; age?: number}
Required
源碼：
type Required<T> = {
[P in keyof T]-?: T[P];
};
實例：
type Person3 = Required<Person>;
// Person3 === {name: string; age: number}
Readonly
源碼：
type Readonly<T> = {
readonly [P in keyof T]: T[P];
};
實例：
type Person4 = Readonly<Person>;
// Person4 === {readonly name: string; readonly age?: number}
Pick
源碼：
type Pick<T, K extends keyof T> = {
[P in K]: T[P];
};
實例：
type Person5 = Pick<Person, 'name'>;
// Person5 === {name: string}
Record
源碼：
type Record<K extends keyof any, T> = {
[P in K]: T;
};
實例：
type Person6 = Record<'name' | 'age', string>;
// Person6 === {name: string; age: string}