这样写是可以的, ts 不报错: interface GetNumber { name: "GetNumber"; } interface GetString { name: "GetString"; } function get(options: GetNumber): number function get(options: GetString): string function get(options: GetNumber | GetString) { switch (options.name) { case "GetNumber": return 1 + 1 case "GetString": return `${1 + 1}` default: throw new Error("param error") } }
下面这样不行, ts 报错: Type 'string | number' is not assignable to type 'number'. // 可是我的 FuncGet 类型 是从另一个文件里引入的 // 做不到像上面那么写 // 那么我该怎么写呢？ interface FuncGet { (options: GetNumber): number; (options: GetString): string; } // ts 编译错误: Type 'string | number' is not assignable to type 'number const get: FuncGet = (options: GetNumber | GetString) => { switch (options.name) { case "GetNumber": return 1 + 1 case "GetString": return `${1 + 1}` default: throw new Error("param error") } }