feat(Android/iOS postMessage): refactoring the old postMessage implementation (#303)

fixes #29
fixes #272
fixes #221
fixes #105
fixes #66

BREAKING CHANGE: Communication from webview to react-native has been completely rewritten. React-native-webview will not use or override window.postMessage anymore. Reasons behind these changes can be found throughout so many issues that it made sense to go that way.

Instead of using window.postMessage(data, *), please now use window.ReactNativeWebView.postMessage(data).

Side note: if you wish to keep compatibility with the old version when you upgrade, you can use the injectedJavascript prop to do that:

const injectedJavascript = `(function() {
  window.postMessage = function(data) {
    window.ReactNativeWebView.postMessage(data);
  };
})()`;

Huge thanks to @jordansexton and @KoenLav!

android/src/main/java/com/reactnativecommunity/webview/RNCWebViewManager.java

 
   protected static final String HTML_ENCODING = "UTF-8";
   protected static final String HTML_MIME_TYPE = "text/html";
-  protected static final String BRIDGE_NAME = "__REACT_WEB_VIEW_BRIDGE";
+  protected static final String JAVASCRIPT_INTERFACE = "ReactNativeWebview";
 
   protected static final String HTTP_METHOD_POST = "POST";
 
 
       if (!mLastLoadFailed) {
         RNCWebView reactWebView = (RNCWebView) webView;
+
         reactWebView.callInjectedJavaScript();
-        reactWebView.linkBridge();
+
         emitFinishEvent(webView, url);
       }
     }
         mContext = c;
       }
 
+      /**
+       * This method is called whenever JavaScript running within the web view calls:
+       *   - window[JAVASCRIPT_INTERFACE].postMessage
+       */
       @JavascriptInterface
       public void postMessage(String message) {
         mContext.onMessage(message);
       }
 
       messagingEnabled = enabled;
+
       if (enabled) {
-        addJavascriptInterface(createRNCWebViewBridge(this), BRIDGE_NAME);
-        linkBridge();
+        addJavascriptInterface(createRNCWebViewBridge(this), JAVASCRIPT_INTERFACE);
       } else {
-        removeJavascriptInterface(BRIDGE_NAME);
+        removeJavascriptInterface(JAVASCRIPT_INTERFACE);
       }
     }
 
       }
     }
 
-    public void linkBridge() {
-      if (messagingEnabled) {
-        if (ReactBuildConfig.DEBUG && Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
-          // See isNative in lodash
-          String testPostMessageNative = "String(window.postMessage) === String(Object.hasOwnProperty).replace('hasOwnProperty', 'postMessage')";
-          evaluateJavascript(testPostMessageNative, new ValueCallback<String>() {
-            @Override
-            public void onReceiveValue(String value) {
-              if (value.equals("true")) {
-                FLog.w(ReactConstants.TAG, "Setting onMessage on a WebView overrides existing values of window.postMessage, but a previous value was defined");
-              }
-            }
-          });
-        }
-
-        evaluateJavascriptWithFallback("(" +
-          "window.originalPostMessage = window.postMessage," +
-          "window.postMessage = function(data) {" +
-            BRIDGE_NAME + ".postMessage(String(data));" +
-          "}" +
-        ")");
-      }
-    }
-
     public void onMessage(String message) {
       dispatchEvent(this, new TopMessageEvent(this.getId(), message));
     }

docs/Reference.md

 
 ### `onMessage`
 
-A function that is invoked when the webview calls `window.postMessage`. Setting this property will inject a `postMessage` global into your webview, but will still call pre-existing values of `postMessage`.
+Function that is invoked when the webview calls `window.ReactNativeWebview.postMessage`. Setting this property will inject this global into your webview.
 
-`window.postMessage` accepts one argument, `data`, which will be available on the event object, `event.nativeEvent.data`. `data` must be a string.
+`window.ReactNativeWebview.postMessage` accepts one argument, `data`, which will be available on the event object, `event.nativeEvent.data`. `data` must be a string.
 
 | Type     | Required |
 | -------- | -------- |

ios/RNCUIWebView.m

 
 NSString *const RNCJSNavigationScheme = @"react-js-navigation";
 
-static NSString *const kPostMessageHost = @"postMessage";
+static NSString *const MessageHandlerName = @"ReactNativeWebview";
 
 @interface RNCUIWebView () <UIWebViewDelegate, RCTAutoInsetsProtocol>
 
     @"data": message,
   };
   NSString *source = [NSString
-    stringWithFormat:@"document.dispatchEvent(new MessageEvent('message', %@));",
+    stringWithFormat:@"window.dispatchEvent(new MessageEvent('message', %@));",
     RCTJSONStringify(eventInitDict, NULL)
   ];
   [_webView stringByEvaluatingJavaScriptFromString:source];
     }
   }
 
-  if (isJSNavigation && [request.URL.host isEqualToString:kPostMessageHost]) {
+  if (isJSNavigation && [request.URL.host isEqualToString:MessageHandlerName]) {
     NSString *data = request.URL.query;
     data = [data stringByReplacingOccurrencesOfString:@"+" withString:@" "];
     data = [data stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
       @"data": data,
     }];
 
-    NSString *source = @"document.dispatchEvent(new MessageEvent('message:received'));";
+    NSString *source = [NSString stringWithFormat:@"window.%@.messageReceived();", MessageHandlerName];
 
     [_webView stringByEvaluatingJavaScriptFromString:source];
 
 - (void)webViewDidFinishLoad:(UIWebView *)webView
 {
   if (_messagingEnabled) {
-    #if RCT_DEV
-    // See isNative in lodash
-    NSString *testPostMessageNative = @"String(window.postMessage) === String(Object.hasOwnProperty).replace('hasOwnProperty', 'postMessage')";
-    BOOL postMessageIsNative = [
-      [webView stringByEvaluatingJavaScriptFromString:testPostMessageNative]
-      isEqualToString:@"true"
-    ];
-    if (!postMessageIsNative) {
-      RCTLogError(@"Setting onMessage on a WebView overrides existing values of window.postMessage, but a previous value was defined");
-    }
-    #endif
     NSString *source = [NSString stringWithFormat:
       @"(function() {"
-        "window.originalPostMessage = window.postMessage;"
-
-        "var messageQueue = [];"
-        "var messagePending = false;"
-
-        "function processQueue() {"
-          "if (!messageQueue.length || messagePending) return;"
-          "messagePending = true;"
-          "window.location = '%@://%@?' + encodeURIComponent(messageQueue.shift());"
-        "}"
-
-        "window.postMessage = function(data) {"
-          "messageQueue.push(String(data));"
-          "processQueue();"
-        "};"
-
-        "document.addEventListener('message:received', function(e) {"
-          "messagePending = false;"
-          "processQueue();"
-        "});"
-      "})();", RNCJSNavigationScheme, kPostMessageHost
+       "  var messageQueue = [];"
+       "  var messagePending = false;"
+
+       "  function processQueue () {"
+       "    if (!messageQueue.length || messagePending) return;"
+       "    messagePending = true;"
+       "    document.location = '%@://%@?' + encodeURIComponent(messageQueue.shift());"
+       "  }"
+
+       "  window.%@ = {"
+       "    postMessage: function (data) {"
+       "      messageQueue.push(String(data));"
+       "      processQueue();"
+       "    },"
+       "    messageReceived: function () {"
+       "      messagePending = false;"
+       "      processQueue();"
+       "    }"
+       "  };"
+       "})();", RNCJSNavigationScheme, MessageHandlerName, MessageHandlerName
     ];
     [webView stringByEvaluatingJavaScriptFromString:source];
   }

ios/RNCWKWebView.m

 
 #import "objc/runtime.h"
 
-static NSString *const MessageHanderName = @"ReactNative";
+static NSString *const MessageHandlerName = @"ReactNativeWebview";
 
 // runtime trick to remove WKWebView keyboard default toolbar
 // see: http://stackoverflow.com/questions/19033292/ios-7-uiwebview-keyboard-issue/19042279#19042279
       wkWebViewConfig.processPool = [[RNCWKProcessPoolManager sharedManager] sharedProcessPool];
     }
     wkWebViewConfig.userContentController = [WKUserContentController new];
-    [wkWebViewConfig.userContentController addScriptMessageHandler: self name: MessageHanderName];
+
+    if (_messagingEnabled) {
+      [wkWebViewConfig.userContentController addScriptMessageHandler:self name:MessageHandlerName];
+
+      NSString *source = [NSString stringWithFormat:
+        @"window.%@ = {"
+         "  postMessage: function (data) {"
+         "    window.webkit.messageHandlers.%@.postMessage(String(data));"
+         "  }"
+         "};", MessageHandlerName, MessageHandlerName
+      ];
+
+      WKUserScript *script = [[WKUserScript alloc] initWithSource:source injectionTime:WKUserScriptInjectionTimeAtDocumentStart forMainFrameOnly:YES];
+      [wkWebViewConfig.userContentController addUserScript:script];
+    }
+
     wkWebViewConfig.allowsInlineMediaPlayback = _allowsInlineMediaPlayback;
 #if WEBKIT_IOS_10_APIS_AVAILABLE
     wkWebViewConfig.mediaTypesRequiringUserActionForPlayback = _mediaPlaybackRequiresUserAction
 - (void)removeFromSuperview
 {
     if (_webView) {
-        [_webView.configuration.userContentController removeScriptMessageHandlerForName:MessageHanderName];
+        [_webView.configuration.userContentController removeScriptMessageHandlerForName:MessageHandlerName];
         [_webView removeObserver:self forKeyPath:@"estimatedProgress"];
         [_webView removeFromSuperview];
         _webView = nil;
 
 /**
  * This method is called whenever JavaScript running within the web view calls:
- *   - window.webkit.messageHandlers.[MessageHanderName].postMessage
+ *   - window.webkit.messageHandlers[MessageHandlerName].postMessage
  */
 - (void)userContentController:(WKUserContentController *)userContentController
        didReceiveScriptMessage:(WKScriptMessage *)message
 
 -(void)setHideKeyboardAccessoryView:(BOOL)hideKeyboardAccessoryView
 {
-
     if (_webView == nil) {
         _savedHideKeyboardAccessoryView = hideKeyboardAccessoryView;
         return;
     }
 
     UIView* subview;
+
     for (UIView* view in _webView.scrollView.subviews) {
         if([[view.class description] hasPrefix:@"WK"])
             subview = view;
 {
   NSDictionary *eventInitDict = @{@"data": message};
   NSString *source = [NSString
-    stringWithFormat:@"document.dispatchEvent(new MessageEvent('message', %@));",
+    stringWithFormat:@"window.dispatchEvent(new MessageEvent('message', %@));",
     RCTJSONStringify(eventInitDict, NULL)
   ];
-  [self evaluateJS: source thenCall: nil];
+  [self injectJavaScript: source];
 }
 
 - (void)layoutSubviews
   }];
 }
 
-
 /**
  * Called when the navigation is complete.
  * @see https://fburl.com/rtys6jlb
 - (void)      webView:(WKWebView *)webView
   didFinishNavigation:(WKNavigation *)navigation
 {
-  if (_messagingEnabled) {
-    #if RCT_DEV
-
-    // Implementation inspired by Lodash.isNative.
-    NSString *isPostMessageNative = @"String(String(window.postMessage) === String(Object.hasOwnProperty).replace('hasOwnProperty', 'postMessage'))";
-    [self evaluateJS: isPostMessageNative thenCall: ^(NSString *result) {
-      if (! [result isEqualToString:@"true"]) {
-        RCTLogError(@"Setting onMessage on a WebView overrides existing values of window.postMessage, but a previous value was defined");
-      }
-    }];
-    #endif
-
-    NSString *source = [NSString stringWithFormat:
-      @"(function() {"
-        "window.originalPostMessage = window.postMessage;"
-
-        "window.postMessage = function(data) {"
-          "window.webkit.messageHandlers.%@.postMessage(String(data));"
-        "};"
-      "})();",
-      MessageHanderName
-    ];
-    [self evaluateJS: source thenCall: nil];
-  }
-
   if (_injectedJavaScript) {
     [self evaluateJS: _injectedJavaScript thenCall: ^(NSString *jsEvaluationValue) {
       NSMutableDictionary *event = [self baseEvent];
       event[@"jsEvaluationValue"] = jsEvaluationValue;
+
       if (self.onLoadingFinish) {
         self.onLoadingFinish(event);
       }

ios/RNCWebView.xcworkspace/contents.xcworkspacedata

-// !$*UTF8*$!
-<?xml version="1.0" encoding="UTF-8"?>
-<Workspace
-   version = "1.0">
-   <FileRef
-      location = "group:RNCWebView.xcodeproj">
-   </FileRef>
-</Workspace>

js/WebView.android.js

         }
         thirdPartyCookiesEnabled={this.props.thirdPartyCookiesEnabled}
         domStorageEnabled={this.props.domStorageEnabled}
-        messagingEnabled={typeof this.props.onMessage === 'function'}
         cacheEnabled={this.props.cacheEnabled}
         onMessage={this.onMessage}
+        messagingEnabled={typeof this.props.onMessage === 'function'}
         overScrollMode={this.props.overScrollMode}
         contentInset={this.props.contentInset}
         automaticallyAdjustContentInsets={

js/WebView.ios.js

       source = { uri: this.props.url };
     }
 
-    const messagingEnabled = typeof this.props.onMessage === 'function';
-
     let NativeWebView = nativeConfig.component;
 
     if (this.props.useWebKit) {
         onLoadingFinish={this._onLoadingFinish}
         onLoadingError={this._onLoadingError}
         onLoadingProgress={this._onLoadingProgress}
-        messagingEnabled={messagingEnabled}
         onMessage={this._onMessage}
+        messagingEnabled={typeof this.props.onMessage === 'function'}
         onShouldStartLoadWithRequest={onShouldStartLoadWithRequest}
         scalesPageToFit={scalesPageToFit}
         allowsInlineMediaPlayback={this.props.allowsInlineMediaPlayback}

js/WebViewTypes.js

   onNavigationStateChange?: (event: WebViewNavigation) => mixed,
 
   /**
-   * A function that is invoked when the webview calls `window.postMessage`.
-   * Setting this property will inject a `postMessage` global into your
-   * webview, but will still call pre-existing values of `postMessage`.
+   * Function that is invoked when the webview calls `window.ReactNativeWebview.postMessage`.
+   * Setting this property will inject this global into your webview.
    *
-   * `window.postMessage` accepts one argument, `data`, which will be
-   * available on the event object, `event.nativeEvent.data`. `data`
-   * must be a string.
+   * `window.ReactNativeWebview.postMessage` accepts one argument, `data`, which will be
+   * available on the event object, `event.nativeEvent.data`. `data` must be a string.
    */
   onMessage?: (event: WebViewMessageEvent) => mixed,