title: How to fully clean up the context and canvas in three.js
body: <p>We have an application that also runs on an iPad. Using three.js r100.</p>
  
  <p>It has a "main" and several "popups", each with its own canvas, scene and renderer. The "main" has a scene etc. too that is always shown.</p>
  
  <p>To avoid memory issues, we create all the objects when the popup is opened, and clean up when the popup is closed.
  But on the iPad, the webinfo still shows the canvasses of closed popups.</p>
  
  <p>And after opening/closing several popups we get an error about too many contexts ("There are too many active WebGL contexts on this page, the oldest context will be lost.").
  The first context that is lost is the "main" scene. After that, the system tries to loose a "popup" context. A second error is shown: "WebGL: INVALID_OPERATION: loseContext: context already lost". That seems logical because we did a forceContextLoss() when closing the popup.</p>
  
  <p>At popup close we:</p>
  
  <ul>
  <li>dispose everything (material etc.) in the scene</li>
  <li>dispose the OrbitControl</li>
  <li>dispose the renderer</li>
  <li>forceContextLoss() the renderer</li>
  <li>remove the canvas from the DOM</li>
  </ul>
  
  <p>I suspect the canvas is keeping the contexts from being cleaned up, but maybe I miss something?
  So, how can we fully remove the contexts of the popups?</p>
  
  <p>Thanks, Willem</p>