typescript overload

from.ts

//!overload
constructor(x: number, y: number) {
  this.x = a;
  this.y = b;
}
constructor(v: Vector2) {
  this.x = v.x;
  this.y = v.y;
}

memo.md

https://developer.mozilla.org/ja/docs/JavaScript/Reference/Operators/instanceof

function C(){};
function D(){};
D.prototype = new C();

var c = new C();
var d = new D();

c instanceof C; //true
d instanceof D; //true

それぞれの優先順位を書かないと

to.ts

constructor(x: number, y: number);
constructor(v: Vector2);
constructor(a: any, b?: number) {
    // null, undefined が渡された場合
    if (a == null) {
        this.x = 0;
        this.y = 0;
        return;
    }
    // instanceof でどちらが呼ばれたのか判断
    if (a instanceof Vector2) {
      this.x = a.x;
        this.y = a.y;
    } else {
        this.x = a;
        this.y = b;
    }
}