<input id="btn" type="button" value="BUTTON" onclick="alert(1)"/>
<script>
 var btn = document.getElementById('btn');
 btn.click();
</script>

<div id="d1" style="background:gold;width:50px;height:50px;" onclick="alert(2)"></div>
<script>
 var d1 = document.getElementById('d1');
 d1.click();
</script>

<input id="btn1" type="button" value="BUTTON 1"/>
<input id="btn2" type="button" value="BUTTON 2"/>
<script>
 var addListener = window.addEventListener ?
   function(el, type, fn) { el.addEventListener(type, fn, false); } :
   function(el, type, fn) { el.attachEvent('on' + type, fn); };
 var btn1 = document.getElementById('btn1');
 var btn2 = document.getElementById('btn2');
 btn1.onclick = function(){
   alert(3);
 };
 addListener(btn2, 'click', function() {alert(4)});
 btn1.click();
 btn2.click();
</script>

<input id="btn1" type="button" value="BUTTON 1" onclick="alert(1)"/>
<input id="btn2" type="button" value="BUTTON 2" onclick="alert(2)"/>
<div id="d1" style="background:gold;width:50px;height:50px;" onclick="alert(3)"></div>
<script>
 function dispatch(el, type){
   try{
     var evt = document.createEvent('Event');
     evt.initEvent(type,true,true);
     el.dispatchEvent(evt);
   }catch(e){alert(e)};
 }
 var btn1 = document.getElementById('btn1');
 var btn2 = document.getElementById('btn2');  
 var d1 = document.getElementById('d1');
 dispatch(btn1, 'click');
 dispatch(btn2, 'click');
 dispatch(d1, 'click');
</script>

function triggerClick( el ) {
 var nodeName = el.nodeName,
   safari_chrome = /webkit/.test(navigator.userAgent.toLowerCase());
 if(safari_chrome && (nodeName != 'INPUT' || nodeName != 'BUTTON')) {
   try{
     var evt = document.createEvent('Event');
     evt.initEvent('click',true,true);
     el.dispatchEvent(evt);
   }catch(e){alert(e)};
 }else{
   el.click();
 }
}

function triggerClick( el ) {
 if(el.click) {
   el.click();
 }else{
   try{
     var evt = document.createEvent('Event');
     evt.initEvent('click',true,true);
     el.dispatchEvent(evt);
   }catch(e){alert(e)};    
 }
}