1.索引签名：No index signature with a parameter

No index signature with a parameter of type 'string' was found on type 'IStatusType'

解释：not in type "IStatusType” Argument type is found on "string"的索引签名

• Error setting

// 返回值状态
interface IStatusType{
    
    400:string,
    401:string,
    403:string,
    404:string,
    405:string,
    500:string,
    502:string,
}
// 定义参数
const _status:IStatusType= {
    
    400:"请求错误",
    401:"登录已过期,请重新登录",
    403:"禁止访问",
    404:"接口不存在",
    405:"资源被禁止",
    500:"内部服务器错误",
    502:"网关错误"
}
// Returns the result example：err.response.data.status === 400
 const errStatus:string = err.response.data.status;
/*报错： Element implicitly has an 'any' type because expression of type 'string' can't be used to index type 'IStatusType'. No index signature with a parameter of type 'string' was found on type 'IStatusType' */
 console.log(_status![errStatus]);

• 解决方案：
  修改IStatusTypeType setting 就不会报错了

 interface IStatusType{
    
    [key: string ]: string;
}

2.什么是索引签名

简单来说：It defines the property names in the object、属性值的类型
tip:TypeScript The index signature of must be string 或者 number

interface Foo {
    
  [key: string]: number;
  x: number;
  y: number;
}

或者

索引签名的名称（如：{ [index: string]: { message: string } } 里的 index ）除了可读性外,并没有任何意义.例如：如果有一个用户名,你可以使用 { username: string}: { message: string },这It is helpful for the next developer to understand your code.

const foo: {
    
  [index: string]: {
     message: string };
} = {
    };

// 储存的东西必须符合结构
// ok
foo['a'] = {
     message: 'some message' };

• Limited string literals

通常与 keyof/typeof 一起使用,来获取变量的类型

type Index = 'a' | 'b' | 'c';
type FromIndex = {
     [k in Index]?: number };
const good: FromIndex = {
     b: 1, c: 2 };