JS debounce

debounce.js

function debounce(fn, delay) {
  let timeout;

  return function(...args) {
    const context = this;
    clearTimeout(timeout);
    timeout = setTimeout(() => fn.apply(context, args), delay);
  }
}

// Usage:
function foo() {
  // code here;
}

// fires once per 500 milliseconds.
const elem = document.getElementById('elem');
elem.addEventListener('scroll', debounce(foo, 500));