You have event.preventDefault() available in vanilla javascript as well. In a generic way you can always use return false. If you attach an event handler you are guaranteed to get event agument passed in the handler as opposed to using the onclick or any other attributes of the element (In which case you should rely on the specific event object available in side the handler which you may not get in all browsers, like in IE you would use window.event).

Ex: -

  document.getElementById('someId').addEventListener('click', function(e){ //say this is an anchor

         //do something

        e.preventDefault();

   });

So for all the anchors:

 var anchors = document.getElementsByTagName('a');

 for(i=0, len=anchors.length; i<len; i++){

     anchors[i].addEventListener('click', function(e){e.preventDefault();});

 }