title: How to create an opacity fade()? (  improvement over jQuery)
body: <p>I'm not using JQuery but I know they have functions to do this.  I know how to do this in JQuery but I want a pure js solution.</p>
  
  <p>How can I time vary the CSS opacity setting?  A unix time stamp has precision to 1000 milliseconds...so that might be one way.</p>
  
  <p>Using clearTimeout and setTimeout would be another way.</p>
  
  <p>What is the best way to do this.  I tried looking at <a href="http://code.jquery.com/jquery-1.7.1.js" rel="nofollow noreferrer">JQuery source</a> but could not figure out what they were doing exactly for <code>fadeIn</code> and <code>fadeOut</code>.</p>
  
  <p><strong>Related</strong></p>
  
  <p><a href="https://stackoverflow.com/questions/9151349/how-to-eliminate-unused-arguments">How to eliminate unused arguments in an opacity fade?</a></p>