sdk/lib/html/html_common/conversions_dartium.dart - sdk.git - Git at Google

 part of html_common;

 convertDartToNative_PrepareForStructuredClone(value) =>
     new _StructuredCloneDartium().convertDartToNative_PrepareForStructuredClone(value);

 convertNativeToDart_AcceptStructuredClone(object, {mustCopy: false}) =>
     new _AcceptStructuredCloneDartium().convertNativeToDart_AcceptStructuredClone(object, mustCopy: mustCopy);

 class _StructuredCloneDartium extends _StructuredClone {
   newJsMap() => new js.JsObject(js.context["Object"]);
   putIntoMap(map, key, value) => map[key] = value;
   // TODO(alanknight): Don't create two extra lists to get a fixed-length JS list.
   newJsList(length) => new js.JsArray.from(new List(length));
   cloneNotRequired(e) => e is js.JsObject;
 }

 class _AcceptStructuredCloneDartium extends _AcceptStructuredClone {
   newDartList(length) => new List(length);

   // JsObjects won't be identical, but will be equal only if the underlying
   // Js entities are identical.
   bool identicalInJs(a, b) =>
       (a is js.JsObject) ? a == b : identical(a, b);

   void forEachJsField(jsObject, action) {
     var keys = js.context["Object"].callMethod("keys", [jsObject]);
     for (var key in keys) {
       action(key, jsObject[key]);
     }
   }
 }

 final _dateConstructor = js.context["Date"];
 final _regexConstructor = js.context["RegExp"];

 bool isJavaScriptDate(value) => value is js.JsObject && value.instanceof(_dateConstructor);
 bool isJavaScriptRegExp(value) => value is js.JsObject && value.instanceof(_regexConstructor);
 bool isJavaScriptArray(value) => value is js.JsArray;

 final _object = js.context["Object"];
 final _getPrototypeOf = _object["getPrototypeOf"];
 _getProto(object) {
   return _getPrototypeOf.apply([object]);
 }
 final _objectProto = js.context["Object"]["prototype"];

 bool isJavaScriptSimpleObject(value) {
   if (value is! js.JsObject) return false;
   var proto = _getProto(value);
   return proto == _objectProto || proto == null;
 }
 bool isImmutableJavaScriptArray(value) =>
     isJavaScriptArray(value) && value["immutable$list"] != null;

 final _promiseConstructor = js.context['Promise'];
 bool isJavaScriptPromise(value) => value is js.JsObject && value['constructor'] == _promiseConstructor;

 Future convertNativePromiseToDartFuture(js.JsObject promise) {
   var completer = new Completer();
   var newPromise = promise
     .callMethod("then", [(result) => completer.complete(result)])
     .callMethod("catch", [(result) => completer.completeError(result)]);
   return completer.future;
 }

 convertDartToNative_DateTime(DateTime date) {
   return new js.JsObject(js.context["Date"], [date.millisecondsSinceEpoch]);
 }

 /// Creates a Dart Rectangle from a Javascript object with properties
 /// left, top, width and height. Used internally in Dartium.
 Rectangle make_dart_rectangle(r) =>
     r == null ? null : new Rectangle(
     js.JsNative.getProperty(r, 'left'),
     js.JsNative.getProperty(r, 'top'),
     js.JsNative.getProperty(r, 'width'),
     js.JsNative.getProperty(r, 'height'));

 // Converts a flat Dart map into a JavaScript object with properties this is
 // is the Dartium only version it uses dart:js.
 // TODO(alanknight): This could probably be unified with the dart2js conversions
 // code in html_common and be more general.
 convertDartToNative_Dictionary(Map dict) {
   if (dict == null) return null;
   var jsObject = new js.JsObject(js.JsNative.getProperty(js.context, 'Object'));
   dict.forEach((String key, value) {
     if (value is List) {
       var jsArray = new js.JsArray();
       value.forEach((elem) {
         jsArray.add(elem is Map ? convertDartToNative_Dictionary(elem): elem);
       });
       jsObject[key] = jsArray;
     } else {
       jsObject[key] = value;
     }
   });
   return jsObject;
 }

 // Conversion function place holder (currently not used in dart2js or dartium).
 List convertDartToNative_StringArray(List<String> input) => input;

 // Converts a Dart list into a JsArray. For the Dartium version only.
 convertDartToNative_List(List input) => new js.JsArray()..addAll(input);

 /// Find the underlying JS object for a dart:html Dart object.
 unwrap_jso(dartClass_instance) => js.unwrap_jso(dartClass_instance);

 // Flag to disable JS interop asserts.  Setting to false will speed up the
 // wrap_jso calls.
 bool interop_checks = false;

 /// Wrap a JS object with an instance of the matching dart:html class. Used only in Dartium.
 wrap_jso(jsObject) {
   try {
     if (jsObject is! js.JsObject || jsObject == null) {
       // JS Interop converted the object to a Dart class e.g., Uint8ClampedList.
       // or it's a simple type.
       return jsObject;
     }

     var wrapper = js.getDartHtmlWrapperFor(jsObject);
     // if we have a wrapper return the Dart instance.
     if (wrapper != null && wrapper is! js.JsObject) {
       return wrapper;
     }

     if (jsObject is js.JsArray) {
       var wrappingList = new DartHtmlWrappingList(jsObject);
       js.setDartHtmlWrapperFor(jsObject, wrappingList);
       return wrappingList;
     }

     // Try the most general type conversions on it.
     // TODO(alanknight): We may be able to do better. This maintains identity,
     // which is useful, but expensive. And if we nest something that only
     // this conversion handles, how does that work? e.g. a list of maps of elements.
     var converted = convertNativeToDart_SerializedScriptValue(jsObject);
     if (!identical(converted, jsObject)) {
       return converted;
     }

     var constructor = js.JsNative.getProperty(jsObject, 'constructor');
     if (constructor == null) {
       // Perfectly valid case for JavaScript objects where __proto__ has
       // intentionally been set to null.
       js.setDartHtmlWrapperFor(jsObject, jsObject);
       return jsObject;
     }
     var jsTypeName = js.JsNative.getProperty(constructor, 'name');
     if (jsTypeName is! String || jsTypeName.length == 0) {
       // Not an html type.
       js.setDartHtmlWrapperFor(jsObject, jsObject);
       return jsObject;
     }

     var dartClass_instance;
     var customElementClass = null;
     var extendsTag = "";
     var custom = getCustomElementEntry(jsObject);
     if (custom != null) {
       customElementClass = custom['type'];
       extendsTag = custom['extends'];
     }

     // Only allow custom elements to be created in the html or svg default
     // namespace.
     var func;
     var defaultNS = jsObject['namespaceURI'] == 'http://www.w3.org/1999/xhtml' ||
         jsObject['namespaceURI'] ==  'http://www.w3.org/2000/svg';
     if (customElementClass != null && extendsTag == "" && defaultNS) {
       // The customElementClass is known but we can't create the real class so
       // create the HtmlElement and it will get upgraded when registerElement's
       // createdCallback is called.
       func = getHtmlCreateFunction('HTMLElement');
     } else {
       func = getHtmlCreateFunction(jsTypeName);
       if (func == null) {
         if (jsTypeName == 'auto-binding') {
           func = getHtmlCreateFunction('HTMLTemplateElement');
         } else if (jsObject.toString() == "[object HTMLElement]") {
           // One last ditch effort could be a JS custom element.
           func = getHtmlCreateFunction('HTMLElement');
         }
       }
     }

     // Can we construct a Dart class?
     if (func != null) {
       dartClass_instance = func();

       // Wrap our Dart instance in both directions.
       dartClass_instance.blink_jsObject = jsObject;
       js.setDartHtmlWrapperFor(jsObject, dartClass_instance);
     }

     // TODO(jacobr): cache that this is not a dart:html JS class.
     return dartClass_instance;
   } catch(e, stacktrace){
     if (interop_checks) {
       if (e is DebugAssertException)
         window.console.log("${e.message}\n ${stacktrace}");
       else
         window.console.log("${stacktrace}");
     }
   }

   return null;
 }

 /**
  * Create Dart class that maps to the JS Type, add the JsObject as an expando
  * on the Dart class and return the created Dart class.
  */
 wrap_jso_no_SerializedScriptvalue(jsObject) {
   try {
     if (jsObject is! js.JsObject || jsObject == null) {
       // JS Interop converted the object to a Dart class e.g., Uint8ClampedList.
       // or it's a simple type.
       return jsObject;
     }

     // TODO(alanknight): With upgraded custom elements this causes a failure because
     // we need a new wrapper after the type changes. We could possibly invalidate this
     // if the constructor name didn't match?
     var wrapper = js.getDartHtmlWrapperFor(jsObject);
     if (wrapper != null) {
       return wrapper;
     }

     if (jsObject is js.JsArray) {
       var wrappingList = new DartHtmlWrappingList(jsObject);
       js.setDartHtmlWrapperFor(jsObject, wrappingList);
       return wrappingList;
     }

     var constructor = js.JsNative.getProperty(jsObject, 'constructor');
     if (constructor == null) {
       // Perfectly valid case for JavaScript objects where __proto__ has
       // intentionally been set to null.
       js.setDartHtmlWrapperFor(jsObject, jsObject);
       return jsObject;
     }
     var jsTypeName = js.JsNative.getProperty(constructor, 'name');
     if (jsTypeName is! String || jsTypeName.length == 0) {
       // Not an html type.
       js.setDartHtmlWrapperFor(jsObject, jsObject);
       return jsObject;
     }

     var func = getHtmlCreateFunction(jsTypeName);
     if (func != null) {
       var dartClass_instance = func();
       dartClass_instance.blink_jsObject = jsObject;
       js.setDartHtmlWrapperFor(jsObject, dartClass_instance);
       return dartClass_instance;
     }
     return jsObject;
   } catch(e, stacktrace){
     if (interop_checks) {
       if (e is DebugAssertException)
         window.console.log("${e.message}\n ${stacktrace}");
       else
         window.console.log("${stacktrace}");
     }
   }

   return null;
 }

 /**
  * Create Dart class that maps to the JS Type that is the JS type being
  * extended using JS interop createCallback (we need the base type of the
  * custom element) not the Dart created constructor.
  */
 wrap_jso_custom_element(jsObject) {
   try {
     if (jsObject is! js.JsObject) {
       // JS Interop converted the object to a Dart class e.g., Uint8ClampedList.
       return jsObject;
     }

     // Find out what object we're extending.
     var objectName = jsObject.toString();
     // Expect to see something like '[object HTMLElement]'.
     if (!objectName.startsWith('[object ')) {
       return jsObject;
     }

     var extendsClass = objectName.substring(8, objectName.length - 1);
     var func = getHtmlCreateFunction(extendsClass);
     if (interop_checks)
       debug_or_assert("func != null name = ${extendsClass}", func != null);
     var dartClass_instance = func();
     dartClass_instance.blink_jsObject = jsObject;
     return dartClass_instance;
   } catch(e, stacktrace){
     if (interop_checks) {
       if (e is DebugAssertException)
         window.console.log("${e.message}\n ${stacktrace}");
       else
         window.console.log("${stacktrace}");
     }

     // Problem?
     return null;
   }
 }

 getCustomElementEntry(element) {
   var hasAttribute = false;

   var jsObject;
   var tag = "";
   var runtimeType = element.runtimeType;
   if (runtimeType == HtmlElement) {
     tag = element.localName;
   } else if (runtimeType == TemplateElement) {
     // Data binding with a Dart class.
     tag = element.attributes['is'];
   } else if (runtimeType == js.JsObjectImpl) {
     // It's a Polymer core element (written in JS).
     // Make sure it's an element anything else we can ignore.
     if (element.hasProperty('nodeType') && element['nodeType'] == 1) {
       if (js.JsNative.callMethod(element, 'hasAttribute', ['is'])) {
         hasAttribute = true;
         // It's data binding use the is attribute.
         tag = js.JsNative.callMethod(element, 'getAttribute', ['is']);
       } else {
         // It's a custom element we want the local name.
         tag = element['localName'];
       }
     }
   } else {
     throw new UnsupportedError('Element is incorrect type. Got ${runtimeType}, expected HtmlElement/HtmlTemplate/JsObjectImpl.');
   }

   var entry = _knownCustomElements[tag];
   if (entry != null) {
     // If there's an 'is' attribute then check if the extends tag registered
     // matches the tag if so then return the entry that's registered for this
     // extendsTag or if there's no 'is' tag then return the entry found.
     if ((hasAttribute && entry['extends'] == tag) || !hasAttribute) {
       return entry;
     }
   }

   return null;
 }

 // List of known tagName to DartClass for custom elements, used for upgrade.
 var _knownCustomElements = new Map<String, Map<Type, String>>();

 void addCustomElementType(String tagName, Type dartClass, [String extendTag]) {
   _knownCustomElements[tagName] =
       {'type': dartClass, 'extends': extendTag != null ? extendTag : "" };
 }

 Type getCustomElementType(object) {
   var entry = getCustomElementEntry(object);
   if (entry != null) {
     return entry['type'];
   }
   return null;
 }

 /**
  * Wraps a JsArray and will call wrap_jso on its entries.
  */
 class DartHtmlWrappingList extends ListBase implements NativeFieldWrapperClass2 {
   DartHtmlWrappingList(this.blink_jsObject);

   final js.JsArray blink_jsObject;

   operator [](int index) => wrap_jso(js.JsNative.getArrayIndex(blink_jsObject, index));

   operator []=(int index, value) => blink_jsObject[index] = value;

   int get length => blink_jsObject.length;
   int set length(int newLength) => blink_jsObject.length = newLength;
 }
	part of html_common;

	convertDartToNative_PrepareForStructuredClone(value) =>
	new _StructuredCloneDartium().convertDartToNative_PrepareForStructuredClone(value);

	convertNativeToDart_AcceptStructuredClone(object, {mustCopy: false}) =>
	new _AcceptStructuredCloneDartium().convertNativeToDart_AcceptStructuredClone(object, mustCopy: mustCopy);

	class _StructuredCloneDartium extends _StructuredClone {
	newJsMap() => new js.JsObject(js.context["Object"]);
	putIntoMap(map, key, value) => map[key] = value;
	// TODO(alanknight): Don't create two extra lists to get a fixed-length JS list.
	newJsList(length) => new js.JsArray.from(new List(length));
	cloneNotRequired(e) => e is js.JsObject;
	}

	class _AcceptStructuredCloneDartium extends _AcceptStructuredClone {
	newDartList(length) => new List(length);

	// JsObjects won't be identical, but will be equal only if the underlying
	// Js entities are identical.
	bool identicalInJs(a, b) =>
	(a is js.JsObject) ? a == b : identical(a, b);

	void forEachJsField(jsObject, action) {
	var keys = js.context["Object"].callMethod("keys", [jsObject]);
	for (var key in keys) {
	action(key, jsObject[key]);
	}
	}
	}

	final _dateConstructor = js.context["Date"];
	final _regexConstructor = js.context["RegExp"];

	bool isJavaScriptDate(value) => value is js.JsObject && value.instanceof(_dateConstructor);
	bool isJavaScriptRegExp(value) => value is js.JsObject && value.instanceof(_regexConstructor);
	bool isJavaScriptArray(value) => value is js.JsArray;

	final _object = js.context["Object"];
	final _getPrototypeOf = _object["getPrototypeOf"];
	_getProto(object) {
	return _getPrototypeOf.apply([object]);
	}
	final _objectProto = js.context["Object"]["prototype"];

	bool isJavaScriptSimpleObject(value) {
	if (value is! js.JsObject) return false;
	var proto = _getProto(value);
	return proto == _objectProto \|\| proto == null;
	}
	bool isImmutableJavaScriptArray(value) =>
	isJavaScriptArray(value) && value["immutable$list"] != null;

	final _promiseConstructor = js.context['Promise'];
	bool isJavaScriptPromise(value) => value is js.JsObject && value['constructor'] == _promiseConstructor;

	Future convertNativePromiseToDartFuture(js.JsObject promise) {
	var completer = new Completer();
	var newPromise = promise
	.callMethod("then", [(result) => completer.complete(result)])
	.callMethod("catch", [(result) => completer.completeError(result)]);
	return completer.future;
	}

	convertDartToNative_DateTime(DateTime date) {
	return new js.JsObject(js.context["Date"], [date.millisecondsSinceEpoch]);
	}

	/// Creates a Dart Rectangle from a Javascript object with properties
	/// left, top, width and height. Used internally in Dartium.
	Rectangle make_dart_rectangle(r) =>
	r == null ? null : new Rectangle(
	js.JsNative.getProperty(r, 'left'),
	js.JsNative.getProperty(r, 'top'),
	js.JsNative.getProperty(r, 'width'),
	js.JsNative.getProperty(r, 'height'));

	// Converts a flat Dart map into a JavaScript object with properties this is
	// is the Dartium only version it uses dart:js.
	// TODO(alanknight): This could probably be unified with the dart2js conversions
	// code in html_common and be more general.
	convertDartToNative_Dictionary(Map dict) {
	if (dict == null) return null;
	var jsObject = new js.JsObject(js.JsNative.getProperty(js.context, 'Object'));
	dict.forEach((String key, value) {
	if (value is List) {
	var jsArray = new js.JsArray();
	value.forEach((elem) {
	jsArray.add(elem is Map ? convertDartToNative_Dictionary(elem): elem);
	});
	jsObject[key] = jsArray;
	} else {
	jsObject[key] = value;
	}
	});
	return jsObject;
	}

	// Conversion function place holder (currently not used in dart2js or dartium).
	List convertDartToNative_StringArray(List<String> input) => input;

	// Converts a Dart list into a JsArray. For the Dartium version only.
	convertDartToNative_List(List input) => new js.JsArray()..addAll(input);

	/// Find the underlying JS object for a dart:html Dart object.
	unwrap_jso(dartClass_instance) => js.unwrap_jso(dartClass_instance);

	// Flag to disable JS interop asserts. Setting to false will speed up the
	// wrap_jso calls.
	bool interop_checks = false;

	/// Wrap a JS object with an instance of the matching dart:html class. Used only in Dartium.
	wrap_jso(jsObject) {
	try {
	if (jsObject is! js.JsObject \|\| jsObject == null) {
	// JS Interop converted the object to a Dart class e.g., Uint8ClampedList.
	// or it's a simple type.
	return jsObject;
	}

	var wrapper = js.getDartHtmlWrapperFor(jsObject);
	// if we have a wrapper return the Dart instance.
	if (wrapper != null && wrapper is! js.JsObject) {
	return wrapper;
	}

	if (jsObject is js.JsArray) {
	var wrappingList = new DartHtmlWrappingList(jsObject);
	js.setDartHtmlWrapperFor(jsObject, wrappingList);
	return wrappingList;
	}

	// Try the most general type conversions on it.
	// TODO(alanknight): We may be able to do better. This maintains identity,
	// which is useful, but expensive. And if we nest something that only
	// this conversion handles, how does that work? e.g. a list of maps of elements.
	var converted = convertNativeToDart_SerializedScriptValue(jsObject);
	if (!identical(converted, jsObject)) {
	return converted;
	}

	var constructor = js.JsNative.getProperty(jsObject, 'constructor');
	if (constructor == null) {
	// Perfectly valid case for JavaScript objects where __proto__ has
	// intentionally been set to null.
	js.setDartHtmlWrapperFor(jsObject, jsObject);
	return jsObject;
	}
	var jsTypeName = js.JsNative.getProperty(constructor, 'name');
	if (jsTypeName is! String \|\| jsTypeName.length == 0) {
	// Not an html type.
	js.setDartHtmlWrapperFor(jsObject, jsObject);
	return jsObject;
	}

	var dartClass_instance;
	var customElementClass = null;
	var extendsTag = "";
	var custom = getCustomElementEntry(jsObject);
	if (custom != null) {
	customElementClass = custom['type'];
	extendsTag = custom['extends'];
	}

	// Only allow custom elements to be created in the html or svg default
	// namespace.
	var func;
	var defaultNS = jsObject['namespaceURI'] == 'http://www.w3.org/1999/xhtml' \|\|
	jsObject['namespaceURI'] == 'http://www.w3.org/2000/svg';
	if (customElementClass != null && extendsTag == "" && defaultNS) {
	// The customElementClass is known but we can't create the real class so
	// create the HtmlElement and it will get upgraded when registerElement's
	// createdCallback is called.
	func = getHtmlCreateFunction('HTMLElement');
	} else {
	func = getHtmlCreateFunction(jsTypeName);
	if (func == null) {
	if (jsTypeName == 'auto-binding') {
	func = getHtmlCreateFunction('HTMLTemplateElement');
	} else if (jsObject.toString() == "[object HTMLElement]") {
	// One last ditch effort could be a JS custom element.
	func = getHtmlCreateFunction('HTMLElement');
	}
	}
	}

	// Can we construct a Dart class?
	if (func != null) {
	dartClass_instance = func();

	// Wrap our Dart instance in both directions.
	dartClass_instance.blink_jsObject = jsObject;
	js.setDartHtmlWrapperFor(jsObject, dartClass_instance);
	}

	// TODO(jacobr): cache that this is not a dart:html JS class.
	return dartClass_instance;
	} catch(e, stacktrace){
	if (interop_checks) {
	if (e is DebugAssertException)
	window.console.log("${e.message}\n ${stacktrace}");
	else
	window.console.log("${stacktrace}");
	}
	}

	return null;
	}

	/**
	* Create Dart class that maps to the JS Type, add the JsObject as an expando
	* on the Dart class and return the created Dart class.
	*/
	wrap_jso_no_SerializedScriptvalue(jsObject) {
	try {
	if (jsObject is! js.JsObject \|\| jsObject == null) {
	// JS Interop converted the object to a Dart class e.g., Uint8ClampedList.
	// or it's a simple type.
	return jsObject;
	}

	// TODO(alanknight): With upgraded custom elements this causes a failure because
	// we need a new wrapper after the type changes. We could possibly invalidate this
	// if the constructor name didn't match?
	var wrapper = js.getDartHtmlWrapperFor(jsObject);
	if (wrapper != null) {
	return wrapper;
	}

	if (jsObject is js.JsArray) {
	var wrappingList = new DartHtmlWrappingList(jsObject);
	js.setDartHtmlWrapperFor(jsObject, wrappingList);
	return wrappingList;
	}

	var constructor = js.JsNative.getProperty(jsObject, 'constructor');
	if (constructor == null) {
	// Perfectly valid case for JavaScript objects where __proto__ has
	// intentionally been set to null.
	js.setDartHtmlWrapperFor(jsObject, jsObject);
	return jsObject;
	}
	var jsTypeName = js.JsNative.getProperty(constructor, 'name');
	if (jsTypeName is! String \|\| jsTypeName.length == 0) {
	// Not an html type.
	js.setDartHtmlWrapperFor(jsObject, jsObject);
	return jsObject;
	}

	var func = getHtmlCreateFunction(jsTypeName);
	if (func != null) {
	var dartClass_instance = func();
	dartClass_instance.blink_jsObject = jsObject;
	js.setDartHtmlWrapperFor(jsObject, dartClass_instance);
	return dartClass_instance;
	}
	return jsObject;
	} catch(e, stacktrace){
	if (interop_checks) {
	if (e is DebugAssertException)
	window.console.log("${e.message}\n ${stacktrace}");
	else
	window.console.log("${stacktrace}");
	}
	}

	return null;
	}

	/**
	* Create Dart class that maps to the JS Type that is the JS type being
	* extended using JS interop createCallback (we need the base type of the
	* custom element) not the Dart created constructor.
	*/
	wrap_jso_custom_element(jsObject) {
	try {
	if (jsObject is! js.JsObject) {
	// JS Interop converted the object to a Dart class e.g., Uint8ClampedList.
	return jsObject;
	}

	// Find out what object we're extending.
	var objectName = jsObject.toString();
	// Expect to see something like '[object HTMLElement]'.
	if (!objectName.startsWith('[object ')) {
	return jsObject;
	}

	var extendsClass = objectName.substring(8, objectName.length - 1);
	var func = getHtmlCreateFunction(extendsClass);
	if (interop_checks)
	debug_or_assert("func != null name = ${extendsClass}", func != null);
	var dartClass_instance = func();
	dartClass_instance.blink_jsObject = jsObject;
	return dartClass_instance;
	} catch(e, stacktrace){
	if (interop_checks) {
	if (e is DebugAssertException)
	window.console.log("${e.message}\n ${stacktrace}");
	else
	window.console.log("${stacktrace}");
	}

	// Problem?
	return null;
	}
	}

	getCustomElementEntry(element) {
	var hasAttribute = false;

	var jsObject;
	var tag = "";
	var runtimeType = element.runtimeType;
	if (runtimeType == HtmlElement) {
	tag = element.localName;
	} else if (runtimeType == TemplateElement) {
	// Data binding with a Dart class.
	tag = element.attributes['is'];
	} else if (runtimeType == js.JsObjectImpl) {
	// It's a Polymer core element (written in JS).
	// Make sure it's an element anything else we can ignore.
	if (element.hasProperty('nodeType') && element['nodeType'] == 1) {
	if (js.JsNative.callMethod(element, 'hasAttribute', ['is'])) {
	hasAttribute = true;
	// It's data binding use the is attribute.
	tag = js.JsNative.callMethod(element, 'getAttribute', ['is']);
	} else {
	// It's a custom element we want the local name.
	tag = element['localName'];
	}
	}
	} else {
	throw new UnsupportedError('Element is incorrect type. Got ${runtimeType}, expected HtmlElement/HtmlTemplate/JsObjectImpl.');
	}

	var entry = _knownCustomElements[tag];
	if (entry != null) {
	// If there's an 'is' attribute then check if the extends tag registered
	// matches the tag if so then return the entry that's registered for this
	// extendsTag or if there's no 'is' tag then return the entry found.
	if ((hasAttribute && entry['extends'] == tag) \|\| !hasAttribute) {
	return entry;
	}
	}

	return null;
	}

	// List of known tagName to DartClass for custom elements, used for upgrade.
	var _knownCustomElements = new Map<String, Map<Type, String>>();

	void addCustomElementType(String tagName, Type dartClass, [String extendTag]) {
	_knownCustomElements[tagName] =
	{'type': dartClass, 'extends': extendTag != null ? extendTag : "" };
	}

	Type getCustomElementType(object) {
	var entry = getCustomElementEntry(object);
	if (entry != null) {
	return entry['type'];
	}
	return null;
	}

	/**
	* Wraps a JsArray and will call wrap_jso on its entries.
	*/
	class DartHtmlWrappingList extends ListBase implements NativeFieldWrapperClass2 {
	DartHtmlWrappingList(this.blink_jsObject);

	final js.JsArray blink_jsObject;

	operator [](int index) => wrap_jso(js.JsNative.getArrayIndex(blink_jsObject, index));

	operator []=(int index, value) => blink_jsObject[index] = value;

	int get length => blink_jsObject.length;
	int set length(int newLength) => blink_jsObject.length = newLength;
	}