Ready function that waits for one or more target elements to be on the page before executing callback function

Ready.js

function Ready(target, cb) {
  let observer;
  const config = {
    attributes: true,
    childList: true,
    subtree: true,
    characterData: true
  };
  if (!observer) {
    observer = new MutationObserver(check);
    observer.observe(document.documentElement, config);
    check();
  }
  function check() {
    const element =
      typeof target === 'object'
        ? (target.every((targetEl) => document.querySelector(targetEl)) &&
            target.map((targetEl) => document.querySelector(targetEl))) || [
            null
          ]
        : [document.querySelector(target)];
    if (element.every((el) => !!el) && element.every((el) => !el.ready)) {
      element.forEach((el) => (el.ready = true));
      setTimeout(() => {
        cb();
      }, 50);
    }
  }
}

export default Ready;