Bouncing ball simulation
Using this.r to represent elapsed time is highly unconventional.  I would have guessed that r stood for "radius".  Why not use this.t like a sane programmer?

The draw() function ends with this.r += 2;, which is odd.  Why should the drawing routine manage the passage of time?  I would expect the time to be managed either in reference to the wall clock or to be passed in as a parameter by whatever code calls draw().



These don't look like parabolas to me.  At best, they would be degenerate ones, since this.x never changes.



The placement of the closing brace here:

if(this.y &lt; 0) {
    this.r = 0;}


is weird.  Conventional formatting would be:

if (this.y &lt; 0) {
    this.r = 0;
}