title: How to check if a custom protocol supported
body: <p>We are using software that registers its own protocol. We can run application from browser then by link like:</p>
  
  <pre><code>customprotocol://do_this.
  </code></pre>
  
  <p>but is there a way to check is such custom protocol supported by user`s system? If not we would like to ask user to install software first.</p>
  
  <p>E.g:</p>
  
  <pre><code>if (canHandle ('customprotocol')) {
       // run software
  }
  else {
      // ask to install
  }
  </code></pre>
  
  <p><strong>Edit</strong>
  I know about protocolLong property but it works only in IE.</p>