javascript - find class name by regex -

i want class match key regex, when search btn, :

<div class="btn"> // match     <div class="span4"> // not match         <div class='btnbtn-success'>  // not match          </div>         <div class='   bbtn '>  // not match          </div>         <div class='   bbtn '>  // not match          </div>         <div class='   b  btn '> / match          </div>          <div class='cbbtn '>  // not match          </div>         <div class='btn '>  // match          </div>         <div class=' bbtn '>  // not match          </div>         <div class='    btn'>  // match          </div>         <div class=" btn ">  // match          </div>         <div class='hello btn '>  // match          </div>         <div class="  btn     ">  // match          </div>         <div class=" btn     hello">  // match          </div>         <div class=" btnaa     hello">  // not match          </div>          <div class=" hello btn     hello"> // match          </div>         <div class=" hello btn">  // match          </div>         <div class=" hello btn     hello"> // match          </div>          <div class=" hello btn  ">  // match          </div>         <div class=" btna ">  // not match          </div>         <div class=" btna-success ">  // not match          </div>     </div> </div> 

what best regex find btn class name in code?

not sure if want divs or class names. ll give shot suppose:

/(.*[\s+\"\']btn[\s+\"\'].*)/g 

demo here : http://regex101.com/r/fd6fc4

feel free ask query or clarifications

updated answer

i editing regex make bit complex 1 cover cases people have mentioned in comments. thank people comments in improving it.

improved regex : /(?=<[^>]+(?=[\s+\"\']btn[\s+\"\']).+)([^>]+>)/g

demo here : http://regex101.com/r/qh2hz2