var button1 = document.getElementById("button1");
var button2 = document.getElementById("button2");
button1.onclick = function(){alert("button1");trigger(button2,"onclick");}
button2.onclick = function(){alert("button2");}
function trigger(ele,event)
{ele[event]();}

<div class="ps-image" style="width:300px;height:300px;border:0px sold red; background:url('/images/ps.png')">
<input type="file" id="file" style="filter:alpha(opacity=0);opacity:0;width:100%;height:100%;"/>
</div>