Multiple timeouts not working?

[espruino-discuss]

Posted at 2015-04-27 by joppiesaus

So I'm still enjoying to work on my fruitmachine, but the way I implement multiple timeouts don't seem to work correctly.
Basically, I've 3 LED's, or fruits - or wheels, and I stop them one by one in order of time. When I spin the wheel, I tell it when to stop spinning. It works by just setting the velocity of the wheel to 0.

Wheel.prototype.spin = function(stopt) // stopt = stoptime
{
  this.vel = (2 + Math.random() * 5) / 40; // give the wheel a velocity
  setTimeout(this.stop, stopt); // tell it when to stop
};

Then you have the stop function

Wheel.prototype.stop = function()
{
  this.vel = 0.0;
};

The spinning happens when the user clicks the button. At that time, spin is called(not Wheel.spin)

function spin()
{
  for (var i = 0; i < N_LEDS;) // loop trough all wheels, spin them
  {
    wheels[i].spin((++i * 500));
  }
  
  setTimeout(function(){
     //... other code. It checks some win conditions and lights and stuff after every wheel stopped.
  }, (N_LEDS + 2.5) * 500);

But, only the last setTimeout seems to be called.
What am I doing wrong?

Here's the full code.

[gfwilliams]

Posted at 2015-04-27 by @gfwilliams

Well, one guess is that (like in a browser) setTimeout(); doesn't set the this variable to what you'd expect, so when stop is called from setTimeout(this.stop, stopt); and it tries to do this.vel = 0, it's actually setting vel on the global variable, not on your wheel.

To fix it, try:

Wheel.prototype.spin = function(stopt) // stopt = stoptime
{
  this.vel = (2 + Math.random() * 5) / 40; // give the wheel a velocity
  var wheel = this;
  setTimeout(function() {
    wheel.stop();
  }, stopt); // tell it when to stop
};

There are other ways to do it, but that one is probably the most readable.

[gfwilliams]

Posted at 2015-04-27 by @gfwilliams

Just to add that this is pretty much standard JS. For example:

function Foo(x) { this.baz = x; }
Foo.prototype.bar = function() { return this.baz; };

var f = new Foo("Hello World");
console.log(f.bar());  // prints "Hello World"
function printer(fn) { console.log(fn()); }
printer(f.bar); // prints 'undefined'

[espruino-discuss]

Posted at 2015-04-27 by joppiesaus

Thanks a lot! I often forget those kinds of things. Now it works!

[espruino-discuss]

Posted at 2015-04-27 by @allObjects

@gordon, didn't you recently add .bind()? Would that now be even a better option - resource-wise - and for sure from a point of avoiding globals...?

I guess the code would then look like this:

Wheel.prototype.spin = function(stopt) // stopt = stoptime
{
  this.vel = (2 + Math.random() * 5) / 40; // give the wheel a velocity
  setTimeout(this.stop.bind(this), stopt); // tell it when to stop
};

Adding this .bind() was a great move! Still have to get used to it having started JS with 1.3...

[gfwilliams]

Posted at 2015-04-27 by @gfwilliams

Yes, that works too - and as you say it's more efficient.

It's just that it's not very readable if you don't know what bind does :)

[espruino-discuss]

Posted at 2015-04-28 by @allObjects

...not because I say it, it is because you @gordon made it so! - Credit where - to whom - credit is due!