TypeScript- notice of the combined primary -08-

Statement merger

If the same name defines two functions, interface or class, they will be merged into a Type:

Merge function

Before learning too overloaded, we can use the overloaded define multiple types of functions:

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('');
    }
}

The combined interface

Interface properties when the merger will be merged into a simple interface:

interface Alarm {
    price: number;
}
interface Alarm {
    weight: number;
}

It is equivalent to:

interface Alarm {
    price: number;
    weight: number;
}

Note that the type of merger of the property must be unique :

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'.

The combined method interface, combined with the function as:

interface Alarm {
    price: number;
    alert(s: string): string;
}
interface Alarm {
    weight: number;
    alert(s: string, n: number): string;
}

It is equivalent to:

interface Alarm {
    price: number;
    weight: number;
    alert(s: string): string;
    alert(s: string, n: number): string;
}

The combined class

Merger and merger rules consistent interface class.

• This article refers to xcatliu