# WKScriptMessageHandler An interface for receiving messages from JavaScript code running in a webpage. ``` @MainActor protocol WKScriptMessageHandler : NSObjectProtocol ``` ## Overview Adopt the [`WKScriptMessageHandler`](/documentation/WebKit/WKScriptMessageHandler) protocol when your app needs a way to respond to JavaScript messages in the web view. When JavaScript code sends a message that specifically targets your message handler, WebKit calls your handler’s [`userContentController(_:didReceive:)`](/documentation/WebKit/WKScriptMessageHandler/userContentController(_:didReceive:)) method. Use that method to implement your response. For example, you might update other parts of your app in response to web content changes. To call your message handler from JavaScript, call the function `window.webkit.messageHandlers..postMessage()` in your code. You specify the value of `` when you install your message handler in a [`WKUserContentController`](/documentation/WebKit/WKUserContentController) object. > Note: > If you want to provide a response back to JavaScript, implement your message handler using the ``doc://com.apple.webkit/documentation/WebKit/WKScriptMessageHandlerWithReply`` protocol instead. ## Topics ### Receiving Messages [`userContentController(_:didReceive:)`](/documentation/WebKit/WKScriptMessageHandler/userContentController(_:didReceive:)) Tells the handler that a webpage sent a script message. [`WKScriptMessage`](/documentation/WebKit/WKScriptMessage) An object that encapsulates a message sent by JavaScript code from a webpage. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)