title: Javascript, HTML5 (canvas) progressbar with update
body: <p>I'm looking for the best way to do a progress bar (in my case it's a life bar for a game) in an html5 canvas.</p>
  
  <p>I don't know if it's better to use javascript and dom element, or draw this bar directly in the canvas.</p>
  
  <p>I need an update function, for example <code>myBar.updateValue(40)</code>, and I need to show the new bar without refresh all the page or all the canvas, of course.</p>
  
  <p>Do you know something like that? An existing script? Thanks!</p>