softrecurse

function softRecurse(func) {
  setTimeout(func, 0);
}

var fibonacci = (function() {
  var sum = 0;
  return {
    calc : function(x) {
      sum = 0;
      this.calcHelper(x);
    },
    calcHelper : function(x) {
      if (x == 0) {
        sum += 0;
      } else if (x == 1) {
        sum += 1;
      } else {
        softRecurse(this.calcHelper(x  - 1));
        softRecurse(this.calcHelper(x - 2));
      }
    },
    val : function() {
      return sum;
    }
  }
})();

fibonacci.calc(10)
fibonacci.val()