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。
之前学习过,我们可以使用重载定义多个函数类型:
function reverse(x: number): number;function reverse(x: string): string;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('');}}
接口中的属性在合并时会简单的合并到一个接口中:
interface Alarm {price: number;}interface Alarm {weight: number;}
相当于:
interface Alarm {price: number;weight: number;}
注意,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;}