<div style="width: 50px;height: 50px;background-color: red;"></div><br>
<div style="width: 50px;height: 50px;background-color: red;"></div><br>
<div style="width: 50px;height: 50px;background-color: red;"></div><br>
<div style="width: 50px;height: 50px;background-color: red;"></div>
<script>
 var divs = document.getElementsByTagName('div');
 //console.log(divs);
 for(var i=0;i<divs.length;i++){
     divs[i].onclick = function(){
         this.style.width = '100px';
         this.style.height = '100px';
     }
 }

</script>