<a href="javascript:;" id="btn">click me</a>
<script type="text/javascript" src="jquery.js"></script>
<script type="text/javascript">
 var url = "http://api.flickr.com/services/"
 "feeds/photos_public.gne?tags=car&"
 "tagmode=any&format=json&jsoncallback=?";
 $( "#btn" ).click(function(){
  $.getJSON( url, function( data ){
   alert( data );
  });
 });
</script>

$( "#btn" ).click(function(e){
 $.getJSON( url, function( data ){
  alert( data );
 });
 e.preventDefault();
});