Some example and semi-pseudo tutorial code showing using closures for chaining animations.

closures-tut.js

// the self-calling function is a
// Javascript "module" pattern for
// not leaking stuff into global scope:
(function(){
  // simple closure example

  function loglater(message){
    return function logger(){
      console.log(message); // references outer function's argument
    }
  }

  var logit = loglater('meow'); // returns a function

  // later, regardless of further invocations of loglater
  // with other arguments, this instance still has access
  // to the outer function's environment as it was when it
  // was defined
  loglater("arf");
  loglater("moo");
  loglater("yay");

  logit(); // logs 'meow'
})();


(function(){
  // using closures to chain animations

  // animation functions return true if done
  function moveX(element, x){
    // move element 1px toward x
    return (/* element's x != x */)
  }

  function moveY(element, y){
    // move element 1px toward y
    return (/* element's y != y */)
  }

  function animate(element, animation, arg, callback){
    function step(){
      if(animation(element, arg)){
        if(callback)
          callback();
      } else {
        setTimeout(10, step);
      }
    }
    step();
  }

  var element = /* ... */;

  animate(element, moveX, 500, function(){
    animate(element, moveY, 500);
  });


})();


(function(){
  // another way of chaining by chaining method calls

  // animation functions return true if done
  function moveX(element, x){
    // move element 1px toward x
    return (/* element's x != x */)
  }

  function moveY(element, y){
    // move element 1px toward y
    return (/* element's y != y */)
  }

  function animate(element, animation, arg){
    var callback = null;

    function step(){
      if(animation(element, arg)){
        if(callback != null)
          callback();
      } else {
        setTimeout(10, step);
      }
    }

    step();

    return {
      then: function(){
        // set the outer function's callback variable
        callback = function(){ animate.apply(this, arguments); }
      }
    }
  }

  var element = /* ... */;

  animate(element, moveX, 500).then(element, moveY, 500);

})();



(function(){
  // not using closures:

  function moveX(element, x, callback){
    // ...
    if(/* done */){
      if(callback)
        callback();
    } else {
      setTimeout(100, moveX, element, x, callback);
    }
  }

  function moveY(..){ ... }

  moveX(element, x, function(){
    moveY(element, x);
  });

})();