function fibonacci(n){
 var res1 = 1;
 var res2 = 1;
 var sum = res2;
 for(var i = 1;i < n;i ++){
   sum = res1 + res2;
   res1 = res2;
   res2 = sum;
 }
 return sum;
}

function fibonacci (n) {
 if ( n <= 1 ) {return 1};
 return fibonacci(n - 1) + fibonacci(n - 2);
}

function fibonacci(n, ac1=1,ac2=1){
  if(n<=1){return ac2}
 return fibonacci(n-1, ac2, ac1 + ac2)
}
Generator 函数和for...of循环
// Generator 函数和for...of循环
function* fibonacci() {
 let [prev, curr] = [0, 1];
　　// foo(;;)相当于死循环 等于while(1)
 for (;;) {
  yield curr;
  [prev, curr] = [curr, prev + curr];
 }
}
for (let n of fibonacci()) {
 if (n > 1000) break;
 console.log(n);
}

const fibonacci = function(){
  var mem = [0,1];
  var f = function(n){
    var res = mem[n];
    if(typeof res !== 'number'){
      mem[n] = f(n-1) + f(n-2);
      res = mem[n];
    }
    return res;
  }
  return f;
}();