title: make a live clock with existing time in div with javascript
body: <p>ok lets say we have a website that need a realtime time;</p>
  
  <p>example :</p>
  
  <p><code>&lt;div id="updatetime"&gt;21:12:52&lt;/div&gt;</code></p>
  
  <p>each seconds update hours:m:second.</p>
  
  <p>what i have in minds using the <code>interval function</code> to do long pool and add the sec +1 if to 60 then add + 1 to m and same as hours. but is there a function already solving this problem?</p>
  
  <p><strong>how do you make this <code>21:12:52</code> a moving real clock with javascript that updates each seconds?</strong></p>
  
  <p>i have search google, stackoverflow, many of them tells us how to make the current real time datetime from javascript. but none from an existing time. if there is please do insert the link.</p>