wtfjs

gistfile1.js

var obj = {
   val: 0,
   double: function() {
      function helper() {
         this.val += this.val;  //this refers to global scope
      }
      helper();
   }
};

obj.val = 2;
obj.double(); //doesn't work
//obj.val is still 2

//have to do it like this:
var obj = {
   val: 0,
   double: function() {
      var that = this;
      function helper() {
         that.val += that.val;  //that captured by closure
      }
      helper();
   }
};