how-to-call-javascript-from-native.md

Execute JavaScript code in an in-app message from native code

{% tabs %} {% tab title="iOS" %}

You can execute JavaScript in an in-app message from native code by completing the following steps:

• Implement and assign a MessagingDelegate
• Obtain a reference to the WKWebView
• Call the JavaScript method

Implement and assign a MessagingDelegate

To register a JavaScript event handler with a Message object, you will first need to implement and set a MessagingDelegate.

For more detailed instructions on implementing and using a MessagingDelegate, please read the tutorial on using MessagingDelegate.

Obtain a reference to the WKWebView

In the shouldShowMessage function of the MessagingDelegate, get a reference to the WKWebView used by the message.

Swift

func shouldShowMessage(message: Showable) -> Bool {
    // access to the whole message from the parent
    let fullscreenMessage = message as? FullscreenMessage
    let message = fullscreenMessage?.parent

    let messageWebView = message?.view as? WKWebView

    ...
}

Call the JavaScript method

With a reference to the WKWebView, the instance method evaluateJavaScript(_:completionHandler:) can now be leveraged to call a JavaScript method.

Further details of this API are explained in the Apple documentation - the example below is provided for the purpose of demonstration:

Swift

func shouldShowMessage(message: Showable) -> Bool {
    // access to the whole message from the parent
    let fullscreenMessage = message as? FullscreenMessage
    let message = fullscreenMessage?.parent

    let messageWebView = message?.view as? WKWebView
    messageWebView?.evaluateJavaScript("startTimer();") { result, error in
        if error != nil {
            // handle error
            return
        }

        if result != nil {
            // do something with the result
        }
    }

    ...
}

{% endtab %}

{% tab title="Android" %}

You can execute JavaScript in an in-app message from native code by completing the following steps:

• Implement and assign a MessagingDelegate
• Obtain a reference to the WebView
• Call the JavaScript method

Implement and assign a MessagingDelegate

To register a JavaScript event handler with a Message object, you will first need to implement and set a MessagingDelegate.

For more detailed instructions on implementing and using a MessagingDelegate, please read the tutorial on using MessagingDelegate.

Obtain a reference to the WebView

In the shouldShowMessage function of the MessagingDelegate, get a reference to the WebView created for Javascript interactions.

Java

@Override
public boolean shouldShowMessage(FullscreenMessage fullscreenMessage) {
  // access to the whole message from the parent
  Message message = (Message) fullscreenMessage.getParent();
      
  WebView webView = message.view;
  
  ...
}

Call the JavaScript method

With a reference to the WebView, the instance method public void evaluateJavascript(@NonNull String script, @Nullable ValueCallback<String> resultCallback) can now be leveraged to call a JavaScript method.

Further details of this API are explained in the Android documentation - the example below is provided for the purpose of demonstration:

Java

@Override
public boolean shouldShowMessage(FullscreenMessage fullscreenMessage) {
  // access to the whole message from the parent
  Message message = (Message) fullscreenMessage.getParent();
      
  WebView webView = message.view;
  // webview operations must be run on the ui thread
  webView.post(new Runnable() {
    @Override
    public void run() {
      webView.evaluateJavascript("startTimer()", new ValueCallback<String>() {
        @Override
        public void onReceiveValue(String s) {
          // do something with the content
        }
      });
    }
  });
  
  ...
}

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