SwiftJS

A simple example of how to do communication from javascript in a WKWebView to iOS native and vice versa using Swift 3 without pulling in a full framework like Cordova.

To JS

To make calls from native to javascript, create a Javascript instance with your WKWebView:

class ViewController: UIViewController {
    var webView: WKWebView?
    var javascript: Javascript?

    // ...

    override func viewDidLoad() {
        self.webView = WKWebView(frame: webFrame, configuration: config)
        self.javascript = Javascript(webView: self.webView!)
    }
}

Then wherever you want to run JS from the UI:

// inside some function
self.javascript!.exec("WebView.handleCallFromNative(\(newText))", completion: { (result: JavascriptResult) in
  //example of how to check for an error message
  if let errorMessage = result.errorMessage {
    print(errorMessage)
  }
  else if let retVal = result.returnValue {
    print("Javascript Returned Value: '\(retVal)'")
  }

  print("result: \(result)")
})

To Native

To make calls from your javascript to native some additional set up is required.

1. Create a new NativeMethodManager() and pass it a WKWebViewConfiguration() to work with:

   let config = WKWebViewConfiguration()
   let methodManager = NativeMethodManager(configuration: config)

2. Then, add the methods you want to it using addMethod():

   methodManager.addMethod(name: "callNative", method: { (message) in
     //message is Any? type, so it must be cast.
     if let name = message as? String {
       print ("Quack, \(name)")
     }
     print("Received `callNative` with message: '\(message)'")
   })

3. Now your method will be available from the javascript under the window.webkit.messageHandlers object and can be invoked by calling postMessage() on your object:

   window.webkit.messageHandlers.callNative.postMessage(message);

   In this example callNative is the name of the method we set up in the addMethod(name:method:) call from step 2. If we had named the method squish in step 2, we could have to call window.webkit.messageHandlers.squish.postMessage(message);