In moblie devices' safari, <a href="#" onclick="return false"> doesn't work, why?

In moblie devices' safari, like iphone or ipad, <a href="#" onclick="return false"> doesn't prevent default behaviour, the page was still redirected to '#', why...?
Like these code:

<a href="#" onclick="return false" id="test_a">click me</a>
 
 var elem = document.getElementById('test_a');
 if (elem.addEventListener) {
     elem.addEventListener('click', function() {
         alert('clicked');
     }, false);
 } else {
     elem.attachEvent('onclick', function() {
         alert('clicked');
     });
 }?
 

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