How can I pass variables to a new object in javascript?

Question

I wish to implement this lib:

var timer = new Tock({
      this.callback:  callbackFunction,
      this.interval:  10,
      this.complete:  completeFunction,
});

However, I wish to be able to make dynamic calls:

var milkshake = my_milkshakes[next];  
var timer = new Tock({
      this.callback:  makeMoreMilkshakes(),  // (Call version 2)
      this.interval:  shakeTime,
      this.complete:  bringThemToTheYard 
});

function bringThemToTheYard(){


    return setNextCallbackFunction();
}

The problem here seems to be that I cannot reach outside the scope of the initialization. In Java, I can easily pass arguments to the constructor, except in the case when a function handle is expected.

By abstract I mean that the code is not reusable through reference, but this is admittedly loose terminology.

My goal is to initialize a single new timer call to create new timers. I need 5 different timers. Ideally, a single timer would be enough because the timers are started and stopped in linear time.

My main problem is that I cannot set (for example) this.interval to a dynamic variable x, because I do not know how to pass a value into the constructor.

My implementation was based on the "code" from the documentation below:

var timer = new Tock({
  countdown: true,
  interval: 10,
  callback: someCallbackFunction,
  complete: someCompleteFunction
});

1) Javascript has no notion of "abstract constructors", it's unclear what you mean by that. 2) this.callback as a key of an object doesn't make a whole lot of sense, what's that supposed to be? 3) It's unclear what you're trying to achieve. — deceze
– deceze ♦, Commented Jan 4, 2016 at 14:12
">My goal is to initialize use a single new timer call to create new timers." So you need a kind of factory function? — lleaff
– lleaff, Commented Jan 4, 2016 at 14:20
"Abstract" in OOP typically has a very very very different meaning than "in place"; you better avoid the use of this word to reduce confusion. { this.callback: .. } is still a syntax error. — deceze
– deceze ♦, Commented Jan 4, 2016 at 14:20
I'll just reiterate what @deceze said, it's hard to understand what your problem is exactly. — lleaff
– lleaff, Commented Jan 4, 2016 at 14:22
Regarding your edit: when you do new Tock({...}), you are passing a value to the constructor, namely an object literal containing various properties. But your object literal is malformed, because the keys can only be string literals, not this.something. — lleaff
– lleaff, Commented Jan 4, 2016 at 14:27

phatskat · Accepted Answer · 2016-01-04 14:27:55Z

I'm not too sure you have a grasp on JavaScript and how much it really differs from Java - they are not that similar.

This:

var timer = new Tock({
    this.callback:  makeMoreMilkshakes(),  // (Call version 2)
    this.interval:  shakeTime,
    this.complete:  bringThemToTheYard 
});

Doesn't work in JavaScript. That's a syntax error as you can't use dot notation (.) on the left-hand side of an object definition. It seems like maybe you want something like:

function Tock(config) {
    var defaultCallback = callbackFunction;
    var defaultInterval = 10;
    var defaultComplete = completeFunction;

    this.callback = config.callback || defaultCallback;
    this.interval = config.interval || defaultInterval;
    this.complete = config.complete || defaultComplete;

    /**
     * This could also be written as follows, I just wanted
     * to emphasize how many people write "defaults" in JS
    this.callback = config.callback || callbackFunction;
    this.interval = config.interval || 10;
    this.complete = config.complete || completeFunction;
    */

    // Go on doing stuff....
}

var timer = new Tock({
    callback: makeMoreMilkshakes(),
    interval: shakeTime,
    complete: bringThemToTheYard
});

Also, this line looks off:

    callback: makeMoreMilkshakes(),

This is assigning the result of makeMoreMilkshakes to the callback, not the function itself. If that's intended, then never mind this bit. But I think you want:

    callback: makeMoreMilkshakes,

without the () instead.

noumenal · Accepted Answer · 2016-01-05 08:31:57Z

The solution I was looking for was this:

function startNewTimer(type) {
  var timer = new Tock({});

  var options = null;

  switch (type){
    case "first":
      options.callback = function1;
      options.interval = interval1;
      options.complete = startNewTimer(second);
      break;
    case "second":
      options.callback = function2;
      options.interval = interval2;
      options.complete = startNewTimer(third);
      break;
    case "third":
      options.callback = function3;
      options.interval = interval3;
      options.complete = startNewTimer(fourth);
      break;
    case "fourth":
      options.callback = function4;
      options.interval = interval4;
      options.complete = startNewTimer(first); //Start over from function1
      break;
  }

  timer.callback = options.callback;
  timer.interval = options.interval;
  timer.complete = options.complete;

  timer.start(0);
  out("Starting timer: ".concat(timer.callback));
}

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