title: Trying to add a "check availability" option to my register form
body: <p>I am trying to add a "check availability" option for the username in my register form. </p>
  
  <p>I have tried using the button tag, but my HTML5 validation prevents the code from being run. Here's my form, oversimplified:</p>
  
  <pre><code>&lt;input type='text' required&gt;  
  &lt;!-- The button !--&gt; 
  &lt;button onclick='isAvailable()'&gt;Check Availability &lt;/button&gt;
  &lt;input type='password' required&gt;
  &lt;input type='email' required&gt;
  </code></pre>
  
  <p>If the user does not enter a username, password, and (valid) email, then the browser returns an error when the button is clicked. </p>
  
  <p>I have tried using a link instead, but I don't know how to run my PHP code through it. Can anybody help?</p>