Typescript构造函数，这两种构造对象的方法是等价的吗？

Question

这两种创建/初始化新对象的方式有什么区别吗？或者它们是相同的吗？一种方法比另一种更好吗？

class Person {
  FirstName: string = "";
  LastName: string = "";

  constructor(FN: string, LN: string) {
    this.FirstName = FN;
    this.LastName = LN;
  }
}




var P:Person;

var P = new Person("John", "Smith"); // METHOD #1

var P = {FirstName:"John", LastName:"Smith"};     // METHOD #2

Answer 1

您正在创建的类型存在差异。在第一种情况下，您将创建 Person 的实例，在第二种情况下，您将创建一个与 Person 具有相同形状的对象。

两者之间存在差异，例如 insanceof 的行为不同。

var P1 = new Person("John", "Smith");     
var P2 : Person = {FirstName:"John", LastName:"Smith"};  

console.log(P1 instanceof Person) // true
console.log(P2 instanceof Person) // false

此外，如果您的类具有方法，则需要在使用对象文字初始化时指定它们:

class Person {
    FirstName: string = "";
    LastName: string = "";

    constructor(FN: string, LN: string) {
        this.FirstName = FN;
        this.LastName = LN;
    }
    fullName() { return this.LastName + this.FirstName; }
}
var P2: Person = { FirstName: "John", LastName: "Smith" }; // error fullName missing 
var P3: Person = { FirstName: "John", LastName: "Smith", fullName: Person.prototype.fullName }; // ok

如果该类具有私有(private)属性，则无法构建兼容的对象文字:

class Person {
    FirstName: string = "";
    LastName: string = "";

    constructor(FN: string, LN: string) {
        this.FirstName = FN;
        this.LastName = LN;
    }
    private fullName;
}
var P2: Person = { FirstName: "John", LastName: "Smith" }; // error Property 'fullName' is missing in type
var P3: Person = { FirstName: "John", LastName: "Smith", fullName: ""}; // Property 'fullName' is private in type 'Person' but not in type