Functions Overloading in interface and classes - how to?

Question

I have this interface :

interface IPoint {
    getDist(): string;
    getDist(x: number): any;
}

and I need a class to implement it but I can't get the right syntax to implement the getDist() method in the class..

class Point implements IPoint {
    // Constructor
    constructor (public x: number, public y: number) { }

    pointMethod() { }

    getDist() {
        Math.sqrt(this.x * this.x + this.y * this.y);
    }
    // Static member
    static origin = new Point(0, 0);
}

it says:

Class 'Point' declares interface 'IPoint' but does not implement it: Types of property 'getDist' of types 'Point' and 'IPoint' are incompatible:Call signatures of types '() => void' and '{ (): string; (x: number): any; }' are incompatible

What's the proper way to do this?

Thanks

Answer 1

When you declare the function in the class you need to decorate it with the overloads:

getDist(): string;
getDist(x: number): any;
getDist(x?: number): any {
    // your code
 }

Answer 2

This answer describes how to implement method overloading in TypeScript, and it's not pretty:

interface IPoint {
    getDist(): string;
    getDist(x: number): any;
}

class Point implements IPoint {
    // Constructor
    constructor (public x: number, public y: number) { }

    pointMethod() { }

    getDist(x?: number) {
         if (x && typeof x == "number") {
             return 'foo';
         } else {
             return 'bar';
         }
    }
}

N.B. with the particular combination of declared return types in the interface, you are limited to returning strings from getDist.

Answer 3

also you can use the default value

interface Foo{
    next()
    next(steps: number)
    prev()
    prev(steps: number)
}

next(steps: number = 1) {
    // ...
}

prev(steps: number = 1) {
    // ...
}