Typescript ques：An index signature parameter type cannot be a union type. Consider using a mapped...

Typescript ques：An index signature parameter type cannot be a union type. Consider using a mapped...

写接口类型时，希望一个类型的键值是联合类型中固定的几个

const enum MSGTYPE{ TEXT = 'text', IMAGE = 'image', } // or // type MSGTYPE = 'text' | 'image'; export interface QywxSendMessage = { msg_id: number; msg_name: string; [key: MSGTYPE]: number; }

显然会报错An index signature parameter type cannot be a union type. Consider using a mapped object type instead. ts(1337)

问题及解决方式呢： github/microsoft/Typescript/issues/33440 github/Microsoft/TypeScript/issues/24220 github/Microsoft/TypeScript/issues/2491

export interface QywxSendMessage = { msg_id: number; msg_name: string; [key in MSGTYPE]: number; }

写接口类型时，希望一个类型的键值是联合类型中固定的几个中的一个

type MSGTYPE = 'text' | 'image'; export interface QywxSendMessage = { msg_id: number; msg_name: string; [key: MSGTYPE]: number; // [key: 'text' | 'image']: number; }

显然也会报错An index signature parameter type cannot be a union type. Consider using a mapped object type instead. ts(1337)

那该如何表示呢？如果用？那显然是有问题的

type MSGTYPE<T> = {'text': T } | {'image':T }; export interface QywxSendMessageParams = { msg_id: number; msg_name: string; } export type QywxSendMessage = QywxSendMessageParams & MSGTYPE<number>;