下面是五种实现斐波那契数列的方法

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
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;
}();