Three ways to implement Fibonacci columns in JS

The following is the Javascript basics tutorial column to introduce the three methods of JS to realize the Fibonacci sequence number, I hope it will be helpful to friends in need!

Three methods of implementing Fibonacci columns in JS

How do you realize the Fibonacci series

1,1,2,3,5,8…

f(n)=f(n-1) + f(n-2)

Method 1:

function f(n){
     if(n == 1 || n == 0){
         return 1;
     }
     return f(n-1) + f(n-2);
 }

 index.html

Give two more solutions for comparison

Method 2:

function f(n  ) {
     var arr = [];
     var value = null;

     function _f(n) {
         if (n == 1 || n == 0) {
         return 1;
     }
     if (arr[n])
         return arr[n];
         value = _f(n - 1) + _f(n - 2);
         arr[n] = value;
         return value;
     }
     return _f(n);
 }

 Method 2

Another simpler way is to use array storage

Method 3:

function fn(n) {
      var dp = new Array(n + 1);
      dp[0] = dp[1] = 1;
      for (let i = 2, length = dp.length; i <length; i++) {
           dp[i] = dp[i - 1] + dp[i - 2];
      }
      return dp[n];
 }