Short answer:
var myFunction = function(e) {
var regExp = new RegExp('//'+location.hostname+'($|/)');
var href = this.href; // please notice this replacement here
if (regExp.test(href)) {
e.preventDefault();
var i = (((href.split('?')[1]).split('/')[0]).split('&')[1]).split('=')[1];
activityFeedClick(event,i);
}
}
var links = document.querySelectorAll('a');
for (var i = 0; i < links.length; i++) {
links[i].addEventListener('click', myFunction);
}