Memoize in Typescript from http://inlehmansterms.net/2015/03/01/javascript-memoization/

Memoize.ts

function memoize(fn: any): any {
  console.log('memoize');
  const cache = {};
  return function () {
    const key: string = JSON.stringify(arguments);
    if (cache[key]) {
      console.log(`${key} found in cache`);
      return cache[key];
    }
    else {
      console.log(`${key} not found in cache`);
      const value = fn.apply(this, arguments);
      cache[key] = value;
      return value;
    }
  };
}

const factorial = memoize(function (n: number): number {
  console.log(`working for factorial(${n})`);
  if (n === 1) { 
    return 1 
  };
  return n * factorial(n - 1);
});

console.log(factorial(3));
// memoize
// {"0":3} not found in cache
// working for factorial(3)
// {"0":2} not found in cache
// working for factorial(2)
// {"0":1} not found in cache
// working for factorial(1)
// 6

console.log(factorial(3));
// {"0":3} found in cache
// 6

console.log(factorial(4));
// {"0":4} not found in cache
// working for factorial(4)
// {"0":3} found in cache
// 24

console.log(factorial(3));
// {"0":3} found in cache
// 6