JS面试题---关于算法台阶的问题

var Stairs = new step();
function step(){
  this.n1=1;
  this.n2=2;
  this.total=100;
  this.getFunction = getFunction;
}
function getFunction(){
    for(i=2;i<this.total;i++){
      res = this.n1 + this.n2;
      this.n1 = this.n2;
      this.n2 = res;
    }
  return res;
}
var totalStairs = Stairs.getFunction();
alert(totalStairs)

for(i=2;i<this.total;i++){
   res = this.n1 + this.n2;
   this.n1 = this.n2;
   this.n2 = res;
}