Memoize.js

// Given a function fn, return a memoized version of that function.

// A memoized function is a function that will never be called twice with the same inputs. Instead it will return a cached value.

// You can assume there are 3 possible input functions: sum, fib, and factorial.

// sum accepts two integers a and b and returns a + b. Assume that if a value has already been cached for the arguments (b, a) where a != b, it cannot be used for the arguments (a, b). For example, if the arguments are (3, 2) and (2, 3), two separate calls should be made.
// fib accepts a single integer n and returns 1 if n <= 1 or fib(n - 1) + fib(n - 2) otherwise.
// factorial accepts a single integer n and returns 1 if n <= 1 or factorial(n - 1) * n otherwise.
 

// Example 1:

// Input:
// fnName = "sum"
// actions = ["call","call","getCallCount","call","getCallCount"]
// values = [[2,2],[2,2],[],[1,2],[]]
// Output: [4,4,1,3,2]
// Explanation:
// const sum = (a, b) => a + b;
// const memoizedSum = memoize(sum);
// memoizedSum(2, 2); // "call" - returns 4. sum() was called as (2, 2) was not seen before.
// memoizedSum(2, 2); // "call" - returns 4. However sum() was not called because the same inputs were seen before.
// // "getCallCount" - total call count: 1
// memoizedSum(1, 2); // "call" - returns 3. sum() was called as (1, 2) was not seen before.
// // "getCallCount" - total call count: 2


// Code 

/**
 * @param {Function} fn
 * @return {Function}
 */
function memoize(fn) {
    let cached = {}
    return function(...args) {
        let n = JSON.stringify(args)
        if (n in cached){
             return cached [n]
        }
       else {
        let result = fn.apply(this , args)
        cached [n] = result
        return result
       }
        
    }
}


/** 
 * let callCount = 0;
 * const memoizedFn = memoize(function (a, b) {
 *	 callCount += 1;
 *   return a + b;
 * })
 * memoizedFn(2, 3) // 5
 * memoizedFn(2, 3) // 5
 * console.log(callCount) // 1 
 */