13. Debounce, throttle, memoisation and other utilities

function debounce(fn, ms) {                // run after the user STOPS for ms (search box)
  let timer;
  return function (...args) {
    clearTimeout(timer);
    timer = setTimeout(() => fn.apply(this, args), ms);
  };
}

function throttle(fn, ms) {                // run at most once per ms (scroll, resize)
  let last = 0;
  return function (...args) {
    const now = Date.now();
    if (now - last >= ms) { last = now; fn.apply(this, args); }
  };
}

function memoize(fn) {
  const cache = new Map();
  return arg => cache.has(arg) ? cache.get(arg) : (cache.set(arg, fn(arg)), cache.get(arg));
}

const curry = fn => function curried(...args) {
  return args.length >= fn.length ? fn(...args) : (...more) => curried(...args, ...more);
};