title: Call JavaScript function from native code in WKWebView
body: <p>Using a WKWebView in iOS 8, how can I run a JavaScript function from the native side or otherwise communicate from the native side to JavaScript? There doesn't appear to be a method akin to UIWebView's <code>stringByEvaluatingJavaScriptFromString:</code>.</p>
  
  <p>(I can use <code>- addScriptMessageHandler:name:</code> on the <code>configuration.userContentController</code> object to allow communication from JS to native, but I'm looking for the opposite direction.)</p>