TypeScript - 声明合并
如果定义了两个相同名字的函数、接口或类,那么它们会合并成一个类型:
函数的合并:
function reverse(x: number): number; function reverse(x: string): string; // 合并成 function reverse(x: number | string): number | string { if (typeof x === 'number') { return Number(x.toString().split('').reverse().join('')); } else if (typeof x === 'string') { return x.split('').reverse().join(''); } }
接口的合并:
interface Alarm { price: number; } interface Alarm { weight: number; } // 相当于 interface Alarm { price: number; weight: number; }
合并的属性的类型必须是唯一的:
interface Alarm { price: number; } interface Alarm { price: number; // 虽然重复了,但是类型都是 `number`,所以不会报错 weight: number; }
interface Alarm { price: number; } interface Alarm { price: string; // 类型不一致,会报错 weight: number; } // index.ts(5,3): error TS2403: Subsequent variable declarations must have the same type. Variable 'price' must be of type 'number', but here has type 'string'.
接口中方法的合并,与函数的合并一样:
interface Alarm { price: number; alert(s: string): string; } interface Alarm { weight: number; alert(s: string, n: number): string; }
相当于:
interface Alarm { price: number; weight: number; alert(s: string): string; alert(s: string, n: number): string; }