title: JavaScriptCore broken with iOS 10
body: <p>I'm seeing some very strange behavior with JavaScriptCore on iOS 10. I'm using it to execute some JS script that performs some logic in my application. On iOS 9, everything works fine. However, on iOS 10, the script will run maybe one or twice and then will stop executing with message such as</p>
  
  <blockquote>
    <p>Error compiling builtin: Invalid private name '@undefined'</p>
  </blockquote>
  
  <p>I'm using a single JSVirtualMachine that loads and compiles the JavaScript code once. Then, each time there is a computation to be done by a component, I create a new JSContext which will perform the computation. After debugging a few hours, I noticed that if I don't use a single JSVirtualMachine but rather create a new instance for each component that needs to execute the JS script, it works.</p>
  
  <p>That's very surprising and something I never say on iOS 8 or 9. Is anyone aware of a change on iOS 10 in that regards?</p>
  
  <p>Thanks!</p>