Question

I need a super-readable version of this super simple inheritance in JavaScript. This is some auto-generated code, where I can’t afford to be using external functions or libraries.

What I really want is, assuming Point3d “inherits” from Point, I want something like this:

function Point(x,y) {
  this.x = x;
  this.y = y;
}

function Point3d(x,y,z) {
  Point(x, y);
  this.z = z;
}

Except it doesn’t actually work:

var pt = new Point3d(230,30,11);
// but x and y are in global scope, they should be in pt.x and pt.y :(

One possible option, would in the code generation duplicate all the members — but since Javascript is prototype based, I would imagine this is easy to do properly (if I actually knew Javascript)

Thanks

Answer 1

Apply the Point constructor to the Point3d object using .call().

function Point3d(x,y,z) {
  Point.call(this, x, y);
  this.z = z;
}

http://jsfiddle.net/MSfu5/

The .call method sets the value of this in the function you’re calling.

Here we’re setting it to the new Point 3d object being constructed.

---

If there’s anything on the Point prototype that Point3d should inherit, you can make the Point3d.prototype object an empty instance of Point.