ts中keyof的使用

映射类型

映射类型允许您通过映射属性类型从现有类型创建新类型。现有类型的每个属性都根据您指定的规则进行转换。然后，转换后的属性构成了新类型。

function getProperty<T, K extends keyof T>(obj: T, key: K) {
  return obj[key];
}

const person: Person = {
  age: 21,
  name: "Tobias",
};

// name is a property of person
// --> no error
const name = getProperty(person, "name");

// gender is not a property of person
// --> error
const gender = getProperty(person, "gender");

type Optional<T> = {
  [K in keyof T]?: T[K]
};

const person: Optional<Person> = {
  name: "Tobias"
  // notice how I do not have to specify an age,
  // since age is now of type 'number?' and is therefor optional
};

映射类型