a contrived example of whats happening with the heap and stack. watch the call stack.

heapAndStack.js

var heap = {};
var stack = [];

var callFunction = function (nameFunc, args, lineNumber) {
  var func = heap[nameFunc];
  var stackFrame = {
    funcy: func,
    name: nameFunc,
    args: args,
    env: {},
    return: undefined
  };
  
  stack.push(stack);
  
  var returnValue = func.apply(this, args);
  stackFrame.returnValue = returnValue;
  return stack.pop();
};