webpack-bootstrap-ui-kit/src/js/drivers/google.track.external.links.js

function _gaLt (event) {
  if (typeof ga !== 'function') {
    return
  }

  let el = event.srcElement || event.target

  /* Loop up the DOM tree through parent elements if clicked element is not a link (eg: an image inside a link) */
  while (
    el &&
    (typeof el.tagName === 'undefined' ||
      el.tagName.toLowerCase() != 'a' ||
      !el.href)
  ) {
    el = el.parentNode
  }

  if (el && el.href) {
    /* link */
    const link = el.href
    if (link.indexOf(location.host) == -1 && !link.match(/^javascript:/i)) {
      /* external link */
      /* HitCallback function to either open link in either same or new window */
      const hitBack = function (link, target) {
        target ? window.open(link, target) : (window.location.href = link)
      }
      /* Is target set and not _(self|parent|top)? */
      const target =
        el.target && !el.target.match(/^_(self|parent|top)$/i)
          ? el.target
          : false
      /* send event with callback */
      ga(
        'send',
        'event',
        'Outgoing Links',
        link,
        document.location.pathname + document.location.search,
        { hitCallback: hitBack(link, target) }
      )

      /* Prevent standard click */
      event.preventDefault ? event.preventDefault() : (event.returnValue = !1)
    }
  }
}

/* Attach the event to all clicks in the document after page has loaded */
const w = window
w.addEventListener
  ? w.addEventListener(
    'load',
    () => {
      document.body.addEventListener('click', _gaLt, !1)
    },
    !1
  )
  : w.attachEvent &&
    w.attachEvent('onload', () => {
      document.body.attachEvent('onclick', _gaLt)
    })