Adjust div width with js

HTML

<div class="bar">
 blabla
</div>

<div class="bar">
 blabla
</div>

CSS

div{
  background-color:green;
}

JavaScript

var bar = document.querySelectorAll('.bar');
	for (var i=0; i < bar.length; i++) {
     bar[i].setAttribute("style", "width:40px");
	}