Improve running in iframes.

dart/site/try/src/iframe_error_handler.dart

+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library trydart.iframe_error_handler;
+
+// TODO(ahe): Remove this import if issue 17936 is fixed.
+import 'dart:js' as hack;
+
+import 'dart:html' show
+    Event,
+    IFrameElement,
+    window;
+
+import 'dart:async' show
+    Stream,
+    StreamController;
+
+class ErrorMessage {
+  final String message;
+  final String filename;
+  final num lineno;
+  final num colno;
+  final String stack;
+
+  ErrorMessage(
+      this.message, this.filename, this.lineno, this.colno, this.stack);
+
+  String toString() {
+    String result = filename == null ? '' : filename;
+    if (lineno != null && lineno != 0 && !lineno.isNaN) {
+      result += ':$lineno';
+    }
+    if (colno != null && colno != 0 && !colno.isNaN) {
+      result += ':$colno';
+    }
+    if (message != null && !message.isEmpty) {
+      if (!result.isEmpty) {
+        result += ': ';
+      }
+      result += message;
+    }
+    if (stack != null && !stack.isEmpty) {
+      if (!result.isEmpty) {
+        result += '\n';
+      }
+      result += stack;
+    }
+    return result;
+  }
+}
+
+Stream<ErrorMessage> errorStream(IFrameElement iframe) {
+  StreamController<ErrorMessage> controller =
+      new StreamController<ErrorMessage>();
+  void onError(
+      String message,
+      String filename,
+      int lineno,
+      [int colno,
+       error]) {
+    // See:
+    // https://mikewest.org/2013/08/debugging-runtime-errors-with-window-onerror
+    String stack;
+    if (error != null) {
+      var jsStack = error['stack'];
+      if (jsStack != null) {
+        stack = hack.context.callMethod('String', [jsStack]);
+      }
+    }
+    controller.add(new ErrorMessage(message, filename, lineno, colno, stack));
+  }
+
+  void installErrorHandler() {
+    // This method uses dart:js to install an error event handler on the content
+    // window of [iframe]. This is a workaround for http://dartbug.com/17936.
+    var iframeProxy = new hack.JsObject.fromBrowserObject(iframe);
+    var contentWindowProxy = iframeProxy['contentWindow'];
+    if (contentWindowProxy == null) {
+      String message =
+          'No contentWindow, call this method *after* adding iframe to'
+          ' document.';
+      window.console.error(message);
+      throw message;
+    }
+
+    // Note: we have two options, use "iframe.contentWindow.onerror = ..." or
+    // "iframe.contentWindow.addEventListener('error', ...)".  The former seems
+    // to provide more details on both Chrome and Firefox (which provides no
+    // information at all in error events).
+    contentWindowProxy['onerror'] = onError;
+  }
+  iframe.onLoad.listen((Event event) => installErrorHandler());
+  installErrorHandler();
+  return controller.stream;
+}