OpenC3/cosmos

export default function on(elSelector, eventName, selector, fn) {
  const element =
    elSelector === 'document' ? document : document.querySelector(elSelector)

  element.addEventListener(eventName, (event) => {
    const possibleTargets = element.querySelectorAll(selector)
    const { target } = event

    for (let i = 0, l = possibleTargets.length; i < l; i += 1) {
      let el = target
      const p = possibleTargets[i]

      while (el && el !== element) {
        if (el === p) {
          fn.call(p, event)
        }
        el = el.parentNode
      }
    }
  })
}