[ufo]

They mentioned memory leaks as their reasoning. Run the following program in any browser and you will see the memory usage balloon out of control:

    var theThing = null;

    function replaceThing(){
      var oldThing = theThing;
      function unused(){ return oldThing }
      theThing = {
        longStr: new Array(1000000).join('*'),
        someMethod: function(){ }
      };
    }

    setInterval(replaceThing, 1000);

V8 (and all other engines I tested) will save the oldThing variable in someMethod's lexical environment record, causing each Thing to keep a reference to the previous Thing, preventing it from being garbage collected. This is despite the fact that the old thing is actually unreachable - someMethod never uses the oldThing variable.

For a more detailed explanation, check out the post that I lifted this example from: http://point.davidglasser.net/2013/06/27/surprising-javascri...

[danneu]

Example of Google's Closure Compiler eliminating the memory leak:

    var theThing = null; 

    function replaceThing() {
      theThing = {
        longStr: Array(1E6).join("*"),
        someMethod: function() { }
      }; 
    } 

    setInterval(replaceThing, 1E3);

http://closure-compiler.appspot.com/home