title: JavaScript toISOString() doesn't work in IE and Firefox
body: <p>I am writing a date validation function by using JavaScript.</p>
  
  <pre><code>function dateCheck(dateString) {
     try {
        return null != new Date(dateString).toISOString();
     }
     catch (error) {
        return false;
     }
  }
  </code></pre>
  
  <p>This function works fine in Chrome, however, in IE and Firefox, I input an invalid date like "11/32/2015", it will regard it as "12/2/2015". I put an invalid date like "23/1/2015", it will regard it as "11/1/2016". I thought toISOString() function can return null if the input date is invalid, but it seems it doesn't.</p>