A surprising JavaScript memory leak found at Meteor(point.davidglasser.net)

  var run = function () {
    var str = new Array(10000000).join('*');
    var fn  = function() {
      str;
    }
    var fn = function() { }
    setInterval(fn, 100);
  };
  setInterval(run, 1000);

    var theThing = null;
    var replaceThing = function () {
      var originalThing = theThing;
      // Define a closure that references originalThing but doesn't ever actually
      // get called. But because this closure exists, originalThing will be in the
      // lexical environment for all closures defined in replaceThing, instead of
      // being optimized out of it. If you remove this function, there is no leak.
      var unused = function () {
        if (originalThing)
          console.log("hi");
      };
      theThing = {
        longStr: new Array(1000000).join('*'),
        // While originalThing is theoretically accessible by this function, it
        // obviously doesn't use it. But because originalThing is part of the
        // lexical environment, someMethod will hold a reference to originalThing,
        // and so even though we are replacing theThing with something that has no
        // effective way to reference the old value of theThing, the old value
        // will never get cleaned up!
        someMethod: function () {}
      };
      // If you add `originalThing = null` here, there is no leak.
    };
    setInterval(replaceThing, 1000);