title: setAttribute() doesn't work the way I expect it to
body: <p>this line of code:</p>
  
  <pre><code>document.getElementById('01').getElementsByTagName("input")[0].setAttribute("value", "1");
  </code></pre>
  
  <p>works perfectly fine when "input" doesn't already have a value. but when the input already has a value, it wouldn't change the value. why is that? </p>