Using addEventListener and getElementsByClassName to pass an element id

You can get the id from the element that responded to the click event with this.id:

var items = document.getElementsByClassName('menu');
for (var i = 0; i < items.length; i++) {
  items[i].addEventListener('click', printDetails);
}

function printDetails(e) {
  console.log("Clicked " + this.id);
}

<ul>
   <li class="menu" id="bob">Robert Smith</li>
   <li class="menu" id="jane">Jane Doe</li>
   <li class="menu" id="sue">Susan Carter</li>
</ul>

codepen demo

var userSelection = document.getElementsByClassName('menu');

for(var i = 0; i < userSelection.length; i++) {
  (function(index) {
    userSelection[index].addEventListener("click", function() {
       console.log("Clicked index: " + index);
     })
  })(i);
}

As pointed out by @torazaburo in the comments, you can use the following if the browsers you want to support are complying with ECMAScript 6 (ES6), the newest version of JavaScript.

var userSelection = document.getElementsByClassName('menu');

for(let i = 0; i < userSelection.length; i++) {
  userSelection[i].addEventListener("click", function() {
    console.log("Clicked index: " + i);
  })
}