Memory function to optimize the performance of functions ----

// used to demonstrate the factorial of n      data stored on the step of the calculation, the next calculation time to determine whether there were last performed, and if there is direct access to the stored value is calculated and then the next step

// n! n*(n-1)*....*2*1

// 0! = 1

// n! = n*(n-1)!

// achieve before memory
      var count = 0 // number of executions
      function factorial(n) {
        count ++
        if(n == 0 || n==1) {
          return 1
        }
        return n * factorial(n-1)
      }
      for(var i=1; i<=5; i++) {
        console.log(factorial(i))
      }

// realize the memory 
        var COUNT = 0　　// number of executions 
        var Cache = []　　// save up --- performed such data calculated from the 5, 6 and then only when the factorial performing 6x5! Is the factorial of 5 directly from the stored data

        function factorial(n) {
            count++
            IF (cache [n-]) { // if the cache (cache value) direct access to the value in the buffer
                return cache[n]
            The else {}　　// is not calculated
                if (n == 0 || n == 1) {
                    cache[0] = 1
                    cache[1] = 1
                    return 1
                } else {
                    cache[n] = n * factorial(n - 1)
                    return cache[n]
                }
            }
        }

        console.time('3')
        console.log(factorial(3))
        console.timeEnd ( '3')
        console.log('=================')
        console.time('4')
        console.log(factorial(4))
        console.timeEnd ( '4')

　　

// 优化
        function factorial(n) {
            if (n == 0 || n == 1) {
                return 1
            } else {
                return n * factorial(n - 1)
            }
        }
        // wrapper function 
        function Memorize (Fn) {
             var Cache = {} // used to store the value of the object 
            return  function () {
                 var key = + Array.prototype.join.call The arguments.length (arguments) // achieve unique key identification 
                IF (Cache [Key]) {
                     return Cache [Key]
                } The else { // use argumens array parameter to obtain a class of 
                    Cache [Key] = fn.apply ( the this , arguments)
                     return Cache [Key]
                }
            }
        }
        var newF = memorize(factorial)