15.readonly常量

readonly定义的常量不可修改

1.

class Http{
    public static readonly baseUrl="https://www.douban.com";
    public static str:string='lisi'
}
Http.str='cheng';
Http.baseUrl='name'  //不可修改

2.interface封装常量

interface attrs{
     readonly id:number;
     name:string;
     //可选属性
     age?:number
}
var obj:attrs={
    id:123456,
   name:'list'
}
obj.name='zhang'
obj.id=123   ///不可修改 报错