为什么Typescript接口不能在Javascript中呈现

我已经用Typescript工作了一个星期，现在我被卡住了，在这里我无法弄清楚Typescript是如何将一个接口转换成javascript的，而编译后它不会出现在javascript代码中

Typescript

interface IPerson { 
firstName:string, 
lastName:string, 
sayHi: ()=>string 
} 



var customer:IPerson = { 
    firstName:"Tom",
    lastName:"Hanks", 
    sayHi: ():string =>{return "Hi there"} 
 } 

 console.log("Customer Object ") 
 console.log(customer.firstName) 
 console.log(customer.lastName) 
 console.log(customer.sayHi())  

var customer = {
firstName: "Tom",
lastName: "Hanks",
sayHi: function () { return "Hi there"; }
};
console.log("Customer Object ");
console.log(customer.firstName);
console.log(customer.lastName);
console.log(customer.sayHi());

Javascript

interface IPerson { 
firstName:string, 
lastName:string, 
sayHi: ()=>string 
} 



var customer:IPerson = { 
    firstName:"Tom",
    lastName:"Hanks", 
    sayHi: ():string =>{return "Hi there"} 
 } 

 console.log("Customer Object ") 
 console.log(customer.firstName) 
 console.log(customer.lastName) 
 console.log(customer.sayHi())  

var customer = {
firstName: "Tom",
lastName: "Hanks",
sayHi: function () { return "Hi there"; }
};
console.log("Customer Object ");
console.log(customer.firstName);
console.log(customer.lastName);
console.log(customer.sayHi());

---

普通JavaScript中不存在接口之类的概念。接口仅存在于TypeScript中，用于保证用法和定义符合合同

interface Post {
  id: string;
  title: string;
}

编译器使用上述定义来保证合同得到遵守：

const goingToNewYork: Post = {
  id: '123-455-222-111',
}

完成类型检查后，typescript只需将ts编译为纯javascript（省略声明）

• 声明可以输出到单独的文件，通常称为

  d.ts

  ：

它不会将接口转换为JS。TS只存在于编译时，在运行时它只存在于JS中。