Constructor overload in TypeScript

Question

Has anybody done constructor overloading in TypeScript. On page 64 of the language specification (v 0.8), there are statements describing constructor overloads, but there wa

Answer 1

Your Box class is attempting to define multiple constructor implementations.

Only the last constructor overload signature is used as the class constructor implementation.

In the below example, note the constructor implementation is defined such that it does not contradict either of the preceding overload signatures.

interface IBox = {
    x: number;
    y: number;
    width: number;
    height: number;
}

class Box {
    public x: number;
    public y: number;
    public width: number;
    public height: number;

    constructor() /* Overload Signature */
    constructor(obj: IBox) /* Overload Signature */
    constructor(obj?: IBox) /* Implementation Constructor */ {
        if (obj) {
            this.x = obj.x;
            this.y = obj.y;
            this.width = obj.width;
            this.height = obj.height;
        } else {
            this.x = 0;
            this.y = 0;
            this.width = 0;
            this.height = 0
        }
    }

    get frame(): string {
        console.log(this.x, this.y, this.width, this.height);
    }
}

new Box().frame; // 0 0 0 0
new Box({ x:10, y:10, width: 70, height: 120 }).frame; // 10 10 70 120



// You could also write the Box class like so;
class Box {
    public x: number = 0;
    public y: number = 0;
    public width: number = 0;
    public height: number = 0;

    constructor() /* Overload Signature */
    constructor(obj: IBox) /* Overload Signature */
    constructor(obj?: IBox) /* Implementation Constructor */ {
        if (obj) {
            this.x = obj.x;
            this.y = obj.y;
            this.width = obj.width;
            this.height = obj.height;
        }
    }

    get frame(): string { ... }
}