JavaScript debounce function.

debounce.js

function debounce(func, wait = 200, immediate) {
  let timeout = null;
  let context = null;
  let args = null;
  let previous = null;
  let result = null;

  function later() {
    var passed = Date.now() - previous;
    if (passed < wait) {
      timeout = setTimeout(later, wait - passed);
    } else {
      timeout = null;
      if (!immediate) func.apply(context, args);
    }
  }

  return function (...rest) {
    context = this;
    args = rest;
    previous = Date.now();

    if (!timeout) {
      timeout = setTimeout(later, wait);
      if (immediate) result = func.apply(context, args); 
    }

    return result;
  };
}