title: Android WebView - detect whether a JS function is defined
body: <p>I'm writing an HTML/JS application that runs under a WebView on Android. Under certain circumstances the page containing the application may not be loaded, or another page might instead (such as 404 page or similar). In general, I need to run a set of JS functions on the application page or take another set of actions in case the application page didn't load.</p>
  
  <p>I'm trying to detect whether the proper page has loaded by detecting whether the appropriate JS is available, but I can't seem to find any way to do it synchronously - only by calling a JS function and expecting a callback via <code>JavasctiptInterface</code>. While this method is feasible, I'm wondering whether there is a better, more elegant and reliable way to accomplish this.</p>
  
  <p>I certainly can't do this by analyzing the page's URL - it might be the right one but with a wrong content.</p>
  
  <p>Any ideas?</p>