Memoization

    /**
     * Memoization - save the results of your function
     * to improve performance.
     */
    
    const myFunc = (function buildFunc() {
      const memo = {};
    
      const getKey = ([a, b]) => {
        //we are always expecting to get two values
        let key = `${a}-${b}`;
        return key;
      };
    
      return (args) => {
        //this is the function that will be myFunc
        let key = getKey(args);
        if (memo[key]) {
          return memo[key];
        } else {
          let sum = 0;
          for (let i = args[0]; i > 0; i--) {
            sum += args[0] * args[1];
          }
          memo[key] = sum;
          return sum;
        }
      };
    })();
    
    let start = Date.now();
    let result1 = myFunc([9000008, 100001]);
    let result2 = myFunc([9000008, 100001]);
    let result3 = myFunc([9000008, 100001]);
    let result4 = myFunc([9000008, 100001]);
    let result5 = myFunc([9000008, 100001]);
    let result6 = myFunc([9000008, 100001]);
    let result7 = myFunc([9000008, 100001]);
    let end = Date.now();
    console.log(end - start);
    
    start = Date.now();
    result1 = myFunc([9000001, 100001]);
    result2 = myFunc([9000002, 100001]);
    result3 = myFunc([9000003, 100001]);
    result4 = myFunc([9000004, 100001]);
    result5 = myFunc([9000005, 100001]);
    result6 = myFunc([9000006, 100001]);
    result7 = myFunc([9000007, 100001]);
    end = Date.now();
    console.log(end - start);