JS function "memoize": Takes a function, f, and returns a memoized version of f.

memoize.js

// Takes a function, f, and returns a memoized version of f.
// Note: only memoize pure, idempotent functions
var memoize = function (f) {
  let store = new Map();
  
  return function (...args) {
    const k = JSON.stringify(args);
    return (store.has(k) ?
            store.get(k) :
            store.set(k, f(...args)).get(k));
  };
};

/*
Example usage:

var do_sum = function (x, y) {
  console.log('did calculation');
  return x + y;
};

var memoized_do_sum = memoize(do_sum);

memoized_do_sum(3, 12);
// output: "did calculation", 15
memoized_do_sum(3, 12);
// output: 15
memoized_do_sum(3, 12);
// output: 15
*/