title: String regex username or email hanging
body: <p>I have a problem when verifying a username input field.</p>
  
  <p>The regex:</p>
  
  <pre><code>var mailformat = /^\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w{2,4})+$/;
  var letterNumber = /^[0-9a-zA-Z]*$/;
  </code></pre>
  
  <p>The check :</p>
  
  <pre><code>if (!letterNumber.test($('#login_username').val()) 
        &amp;&amp; !mailformat.test($('#login_username').val())){
   ...
  }
  </code></pre>
  
  <p>The browser (chrome and ie) hangs when I want to verify with this entry:</p>
  
  <pre><code>012345678901234567890123456789@
  </code></pre>
  
  <p>Anyone any idea why?</p>
  
  <p>I tried with the regex in one expression, but got the same result.
  (regex are ok because seperately they work)</p>