Rebuilding planck.js used by testbed

[1pakch]

I am porting the Top-down car demo and computing a projection of one vector on another one is quite a common operation there. Hence I implemented a projectOn method for the Vec2 class and the issue is that I am unable to run a testbed so that it picks up the new version of the Vec2 class.

While I am able to rebuild dist/planck.js using gulp so that it includes the new method it is still not picked up by the testbed. Naturally, I am wondering what goes wrong.

I am new to js so I apologize if the issue is trivial.

[shakiba]

Testbed does not use dist/planck.js, it serves and uses a live build. You could check in the browser to see if it is added.

By the way, isn't it possible to use dot function for projection?

[1pakch]

I even see this new method in Developer Tools sources of Vec2 in Chromium. Regardless of this it is undefined on Vec2 objects spit out by the library. I am a complete JS newbie, so maybe my comprehension of what is going on is a bit off.

I meant projection as a vector, i.e.

project = function(v, w) {
    Vec2.assert(v);
    Vec2.assert(w);
    return w.mul(Vec2.dot(v, w));
}

IMO something like v.projectOn(w) reads better as the geometric meaning is immediately clear.

[shakiba]

Can you please include the exact code that you are adding?

You could either do Vec2.projectOn = function(v, w){...} or Vec2.prootype.projectOn = function(w){...} which are a little different. (I recommend studying prototypes in JS if you are new to this topic.)

[1pakch]

It is the exact code except for the name. The issue was that I did not understand the different ways of defining methods in JS. As I see it now

• Vec2.projectOn = function(v, w){...} defines a static method which can only be invoked via Vec2.projectOn(x,y) but not x.projectOn(y).
• Vec2.prototype.projectOn = function(other){...} defines a method for all instances that can be invoked via x.projectOn(y) (and Vec2.prototype.projectOn(x, y) but in this case x will be an Object and not a Vec2)
• One can also define an instance method directly in an object constructor. Unlike the prototype version the implementation code object will not be shared across instances. The benefit is that one can use constructor parameters explicitly which is clearly not possible with prototype methods (one needs pass everything via this).

Many thanks, you pointed me in the right direction. The only thing I am not quite sure about is the call Vec2.prototype.projectOn(x, y). Why and how it works so that x is passed as an Object and not as Vec2? (I guess I should read a bit on JS type system as it is a bit different from what I am used to (Python, C++)).