Wait for DOM elements to exist before executing a callback

wait-for.js

// target can ben an array of targets like ['#element', '.element']
function waitFor(target, callback, timeout = 1000) {
  return new Promise((resolve) => {
    const interval = window.setInterval(() => {
      let isTargetOnDOM

      isTargetOnDOM = Array.isArray(target)
        ? target.every((element) => document.querySelector(element))
        : (isTargetOnDOM = document.querySelector(target))

      if (isTargetOnDOM) {
        callback()
        clearInterval(interval)
        return resolve()
      }
    }, timeout)
  })
}