title: How to check if a URL is valid
body: <p>How can I check if a string is a valid URL?</p>
  
  <p>For example:</p>
  
  <pre><code>http://hello.it =&gt; yes
  http:||bra.ziz, =&gt; no
  </code></pre>
  
  <p>If this is a valid URL how can I check if this is relative to a image file?</p>