Version 0.8.10.2

dart/third_party/pkg/js/lib/js.dart

-// Copyright (c) 2013, 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.
-
-/**
- * The js.dart library provides simple JavaScript invocation from Dart that
- * works on both Dartium and on other modern browsers via Dart2JS.
- *
- * It provides a model based on scoped [Proxy] objects.  Proxies give Dart
- * code access to JavaScript objects, fields, and functions as well as the
- * ability to pass Dart objects and functions to JavaScript functions.  Scopes
- * enable developers to use proxies without memory leaks - a common challenge
- * with cross-runtime interoperation.
- *
- * The top-level [context] getter provides a [Proxy] to the global JavaScript
- * context for the page your Dart code is running on.  In the following example:
- *
- *     import 'package:js/js.dart' as js;
- *
- *     void main() {
- *       js.context.alert('Hello from Dart via JavaScript');
- *     }
- *
- * js.context.alert creates a proxy to the top-level alert function in
- * JavaScript.  It is invoked from Dart as a regular function that forwards to
- * the underlying JavaScript one.  By default, proxies are released when
- * the currently executing event completes, e.g., when main is completes
- * in this example.
- *
- * The library also enables JavaScript proxies to Dart objects and functions.
- * For example, the following Dart code:
- *
- *     js.context.dartCallback = new Callback.once((x) => print(x*2));
- *
- * defines a top-level JavaScript function 'dartCallback' that is a proxy to
- * the corresponding Dart function.  The [Callback.once] constructor allows the
- * proxy to the Dart function to be retained across multiple events;
- * instead it is released after the first invocation.  (This is a common
- * pattern for asychronous callbacks.)
- *
- * Note, parameters and return values are intuitively passed by value for
- * primitives and by reference for non-primitives.  In the latter case, the
- * references are automatically wrapped and unwrapped as proxies by the library.
- *
- * This library also allows construction of JavaScripts objects given a [Proxy]
- * to a corresponding JavaScript constructor.  For example, if the following
- * JavaScript is loaded on the page:
- *
- *     function Foo(x) {
- *       this.x = x;
- *     }
- *
- *     Foo.prototype.add = function(other) {
- *       return new Foo(this.x + other.x);
- *     }
- *
- * then, the following Dart:
- *
- *     var foo = new js.Proxy(js.context.Foo, 42);
- *     var foo2 = foo.add(foo);
- *     print(foo2.x);
- *
- * will construct a JavaScript Foo object with the parameter 42, invoke its
- * add method, and return a [Proxy] to a new Foo object whose x field is 84.
- *
- * See [samples](http://dart-lang.github.com/js-interop/example) for more
- * examples of usage.
- *
- * See this [article](http://www.dartlang.org/articles/js-dart-interop) for
- * more detailed discussion.
- */
-
-library js;
-
-import 'dart:async';
-import 'dart:html';
-import 'dart:isolate';
-import 'dart:mirrors';
-
-// JavaScript bootstrapping code.
-// TODO(vsm): Migrate this to use a builtin resource mechanism once we have
-// one.
-
-// NOTE: Please re-run tools/create_bootstrap.dart on any modification of
-// this bootstrap string.
-final _JS_BOOTSTRAP = r"""
-(function() {
-  // Proxy support for js.dart.
-
-  var globalContext = window;
-
-  // Support for binding the receiver (this) in proxied functions.
-  function bindIfFunction(f, _this) {
-    if (typeof(f) != "function") {
-      return f;
-    } else {
-      return new BoundFunction(_this, f);
-    }
-  }
-
-  function unbind(obj) {
-    if (obj instanceof BoundFunction) {
-      return obj.object;
-    } else {
-      return obj;
-    }
-  }
-
-  function getBoundThis(obj) {
-    if (obj instanceof BoundFunction) {
-      return obj._this;
-    } else {
-      return globalContext;
-    }
-  }
-
-  function BoundFunction(_this, object) {
-    this._this = _this;
-    this.object = object;
-  }
-
-  // Table for local objects and functions that are proxied.
-  function ProxiedObjectTable() {
-    // Name for debugging.
-    this.name = 'js-ref';
-
-    // Table from IDs to JS objects.
-    this.map = {};
-
-    // Generator for new IDs.
-    this._nextId = 0;
-
-    // Counter for deleted proxies.
-    this._deletedCount = 0;
-
-    // Flag for one-time initialization.
-    this._initialized = false;
-
-    // Ports for managing communication to proxies.
-    this.port = new ReceivePortSync();
-    this.sendPort = this.port.toSendPort();
-
-    // Set of IDs that are global.
-    // These will not be freed on an exitScope().
-    this.globalIds = {};
-
-    // Stack of scoped handles.
-    this.handleStack = [];
-
-    // Stack of active scopes where each value is represented by the size of
-    // the handleStack at the beginning of the scope.  When an active scope
-    // is popped, the handleStack is restored to where it was when the
-    // scope was entered.
-    this.scopeIndices = [];
-  }
-
-  // Number of valid IDs.  This is the number of objects (global and local)
-  // kept alive by this table.
-  ProxiedObjectTable.prototype.count = function () {
-    return Object.keys(this.map).length;
-  }
-
-  // Number of total IDs ever allocated.
-  ProxiedObjectTable.prototype.total = function () {
-    return this.count() + this._deletedCount;
-  }
-
-  // Adds an object to the table and return an ID for serialization.
-  ProxiedObjectTable.prototype.add = function (obj) {
-    if (this.scopeIndices.length == 0) {
-      throw "Cannot allocate a proxy outside of a scope.";
-    }
-    // TODO(vsm): Cache refs for each obj?
-    var ref = this.name + '-' + this._nextId++;
-    this.handleStack.push(ref);
-    this.map[ref] = obj;
-    return ref;
-  }
-
-  ProxiedObjectTable.prototype._initializeOnce = function () {
-    if (!this._initialized) {
-      this._initialize();
-      this._initialized = true;
-    }
-  }
-
-  // Enters a new scope for this table.
-  ProxiedObjectTable.prototype.enterScope = function() {
-    this._initializeOnce();
-    this.scopeIndices.push(this.handleStack.length);
-  }
-
-  // Invalidates all non-global IDs in the current scope and
-  // exit the current scope.
-  ProxiedObjectTable.prototype.exitScope = function() {
-    var start = this.scopeIndices.pop();
-    for (var i = start; i < this.handleStack.length; ++i) {
-      var key = this.handleStack[i];
-      if (!this.globalIds.hasOwnProperty(key)) {
-        delete this.map[this.handleStack[i]];
-        this._deletedCount++;
-      }
-    }
-    this.handleStack = this.handleStack.splice(0, start);
-  }
-
-  // Makes this ID globally scope.  It must be explicitly invalidated.
-  ProxiedObjectTable.prototype.globalize = function(id) {
-    this.globalIds[id] = true;
-  }
-
-  // Invalidates this ID, potentially freeing its corresponding object.
-  ProxiedObjectTable.prototype.invalidate = function(id) {
-    var old = this.get(id);
-    delete this.globalIds[id];
-    delete this.map[id];
-    this._deletedCount++;
-  }
-
-  // Gets the object or function corresponding to this ID.
-  ProxiedObjectTable.prototype.get = function (id) {
-    if (!this.map.hasOwnProperty(id)) {
-      throw 'Proxy ' + id + ' has been invalidated.'
-    }
-    return this.map[id];
-  }
-
-  ProxiedObjectTable.prototype._initialize = function () {
-    // Configure this table's port to forward methods, getters, and setters
-    // from the remote proxy to the local object.
-    var table = this;
-
-    this.port.receive(function (message) {
-      // TODO(vsm): Support a mechanism to register a handler here.
-      try {
-        var object = table.get(message[0]);
-        var receiver = unbind(object);
-        var member = message[1];
-        var kind = message[2];
-        var args = message[3].map(deserialize);
-        if (kind == 'get') {
-          // Getter.
-          var field = member;
-          if (field in receiver && args.length == 0) {
-            var result = bindIfFunction(receiver[field], receiver);
-            return [ 'return', serialize(result) ];
-          }
-        } else if (kind == 'set') {
-          // Setter.
-          var field = member;
-          if (args.length == 1) {
-            return [ 'return', serialize(receiver[field] = args[0]) ];
-          }
-        } else if (kind == 'apply') {
-          // Direct function invocation.
-          var _this = getBoundThis(object);
-          return [ 'return', serialize(receiver.apply(_this, args)) ];
-        } else if (member == '[]' && args.length == 1) {
-          // Index getter.
-          var result = bindIfFunction(receiver[args[0]], receiver);
-          return [ 'return', serialize(result) ];
-        } else if (member == '[]=' && args.length == 2) {
-          // Index setter.
-          return [ 'return', serialize(receiver[args[0]] = args[1]) ];
-        } else {
-          // Member function invocation.
-          var f = receiver[member];
-          if (f) {
-            var result = f.apply(receiver, args);
-            return [ 'return', serialize(result) ];
-          }
-        }
-        return [ 'none' ];
-      } catch (e) {
-        return [ 'throws', e.toString() ];
-      }
-    });
-  }
-
-  // Singleton for local proxied objects.
-  var proxiedObjectTable = new ProxiedObjectTable();
-
-  // DOM element serialization code.
-  var _localNextElementId = 0;
-  var _DART_ID = 'data-dart_id';
-  var _DART_TEMPORARY_ATTACHED = 'data-dart_temporary_attached';
-
-  function serializeElement(e) {
-    // TODO(vsm): Use an isolate-specific id.
-    var id;
-    if (e.hasAttribute(_DART_ID)) {
-      id = e.getAttribute(_DART_ID);
-    } else {
-      id = (_localNextElementId++).toString();
-      e.setAttribute(_DART_ID, id);
-    }
-    if (e !== document.documentElement) {
-      // Element must be attached to DOM to be retrieve in js part.
-      // Attach top unattached parent to avoid detaching parent of "e" when
-      // appending "e" directly to document. We keep count of elements
-      // temporarily attached to prevent detaching top unattached parent to
-      // early. This count is equals to the length of _DART_TEMPORARY_ATTACHED
-      // attribute. There could be other elements to serialize having the same
-      // top unattached parent.
-      var top = e;
-      while (true) {
-        if (top.hasAttribute(_DART_TEMPORARY_ATTACHED)) {
-          var oldValue = top.getAttribute(_DART_TEMPORARY_ATTACHED);
-          var newValue = oldValue + "a";
-          top.setAttribute(_DART_TEMPORARY_ATTACHED, newValue);
-          break;
-        }
-        if (top.parentNode == null) {
-          top.setAttribute(_DART_TEMPORARY_ATTACHED, "a");
-          document.documentElement.appendChild(top);
-          break;
-        }
-        if (top.parentNode === document.documentElement) {
-          // e was already attached to dom
-          break;
-        }
-        top = top.parentNode;
-      }
-    }
-    return id;
-  }
-
-  function deserializeElement(id) {
-    // TODO(vsm): Clear the attribute.
-    var list = document.querySelectorAll('[' + _DART_ID + '="' + id + '"]');
-
-    if (list.length > 1) throw 'Non unique ID: ' + id;
-    if (list.length == 0) {
-      throw 'Element must be attached to the document: ' + id;
-    }
-    var e = list[0];
-    if (e !== document.documentElement) {
-      // detach temporary attached element
-      var top = e;
-      while (true) {
-        if (top.hasAttribute(_DART_TEMPORARY_ATTACHED)) {
-          var oldValue = top.getAttribute(_DART_TEMPORARY_ATTACHED);
-          var newValue = oldValue.substring(1);
-          top.setAttribute(_DART_TEMPORARY_ATTACHED, newValue);
-          // detach top only if no more elements have to be unserialized
-          if (top.getAttribute(_DART_TEMPORARY_ATTACHED).length === 0) {
-            top.removeAttribute(_DART_TEMPORARY_ATTACHED);
-            document.documentElement.removeChild(top);
-          }
-          break;
-        }
-        if (top.parentNode === document.documentElement) {
-          // e was already attached to dom
-          break;
-        }
-        top = top.parentNode;
-      }
-    }
-    return e;
-  }
-
-
-  // Type for remote proxies to Dart objects.
-  function DartProxy(id, sendPort) {
-    this.id = id;
-    this.port = sendPort;
-  }
-
-  // Serializes JS types to SendPortSync format:
-  // - primitives -> primitives
-  // - sendport -> sendport
-  // - DOM element -> [ 'domref', element-id ]
-  // - Function -> [ 'funcref', function-id, sendport ]
-  // - Object -> [ 'objref', object-id, sendport ]
-  function serialize(message) {
-    if (message == null) {
-      return null;  // Convert undefined to null.
-    } else if (typeof(message) == 'string' ||
-               typeof(message) == 'number' ||
-               typeof(message) == 'boolean') {
-      // Primitives are passed directly through.
-      return message;
-    } else if (message instanceof SendPortSync) {
-      // Non-proxied objects are serialized.
-      return message;
-    } else if (message instanceof Element &&
-        (message.ownerDocument == null || message.ownerDocument == document)) {
-      return [ 'domref', serializeElement(message) ];
-    } else if (message instanceof BoundFunction &&
-               typeof(message.object) == 'function') {
-      // Local function proxy.
-      return [ 'funcref',
-               proxiedObjectTable.add(message),
-               proxiedObjectTable.sendPort ];
-    } else if (typeof(message) == 'function') {
-      if ('_dart_id' in message) {
-        // Remote function proxy.
-        var remoteId = message._dart_id;
-        var remoteSendPort = message._dart_port;
-        return [ 'funcref', remoteId, remoteSendPort ];
-      } else {
-        // Local function proxy.
-        return [ 'funcref',
-                 proxiedObjectTable.add(message),
-                 proxiedObjectTable.sendPort ];
-      }
-    } else if (message instanceof DartProxy) {
-      // Remote object proxy.
-      return [ 'objref', message.id, message.port ];
-    } else {
-      // Local object proxy.
-      return [ 'objref',
-               proxiedObjectTable.add(message),
-               proxiedObjectTable.sendPort ];
-    }
-  }
-
-  function deserialize(message) {
-    if (message == null) {
-      return null;  // Convert undefined to null.
-    } else if (typeof(message) == 'string' ||
-               typeof(message) == 'number' ||
-               typeof(message) == 'boolean') {
-      // Primitives are passed directly through.
-      return message;
-    } else if (message instanceof SendPortSync) {
-      // Serialized type.
-      return message;
-    }
-    var tag = message[0];
-    switch (tag) {
-      case 'funcref': return deserializeFunction(message);
-      case 'objref': return deserializeObject(message);
-      case 'domref': return deserializeElement(message[1]);
-    }
-    throw 'Unsupported serialized data: ' + message;
-  }
-
-  // Create a local function that forwards to the remote function.
-  function deserializeFunction(message) {
-    var id = message[1];
-    var port = message[2];
-    // TODO(vsm): Add a more robust check for a local SendPortSync.
-    if ("receivePort" in port) {
-      // Local function.
-      return unbind(proxiedObjectTable.get(id));
-    } else {
-      // Remote function.  Forward to its port.
-      var f = function () {
-        var depth = enterScope();
-        try {
-          var args = Array.prototype.slice.apply(arguments);
-          args.splice(0, 0, this);
-          args = args.map(serialize);
-          var result = port.callSync([id, '#call', args]);
-          if (result[0] == 'throws') throw deserialize(result[1]);
-          return deserialize(result[1]);
-        } finally {
-          exitScope(depth);
-        }
-      };
-      // Cache the remote id and port.
-      f._dart_id = id;
-      f._dart_port = port;
-      return f;
-    }
-  }
-
-  // Creates a DartProxy to forwards to the remote object.
-  function deserializeObject(message) {
-    var id = message[1];
-    var port = message[2];
-    // TODO(vsm): Add a more robust check for a local SendPortSync.
-    if ("receivePort" in port) {
-      // Local object.
-      return proxiedObjectTable.get(id);
-    } else {
-      // Remote object.
-      return new DartProxy(id, port);
-    }
-  }
-
-  // Remote handler to construct a new JavaScript object given its
-  // serialized constructor and arguments.
-  function construct(args) {
-    args = args.map(deserialize);
-    var constructor = unbind(args[0]);
-    args = Array.prototype.slice.call(args, 1);
-
-    // Until 10 args, the 'new' operator is used. With more arguments we use a
-    // generic way that may not work, particulary when the constructor does not
-    // have an "apply" method.
-    var ret = null;
-    if (args.length === 0) {
-      ret = new constructor();
-    } else if (args.length === 1) {
-      ret = new constructor(args[0]);
-    } else if (args.length === 2) {
-      ret = new constructor(args[0], args[1]);
-    } else if (args.length === 3) {
-      ret = new constructor(args[0], args[1], args[2]);
-    } else if (args.length === 4) {
-      ret = new constructor(args[0], args[1], args[2], args[3]);
-    } else if (args.length === 5) {
-      ret = new constructor(args[0], args[1], args[2], args[3], args[4]);
-    } else if (args.length === 6) {
-      ret = new constructor(args[0], args[1], args[2], args[3], args[4],
-                            args[5]);
-    } else if (args.length === 7) {
-      ret = new constructor(args[0], args[1], args[2], args[3], args[4],
-                            args[5], args[6]);
-    } else if (args.length === 8) {
-      ret = new constructor(args[0], args[1], args[2], args[3], args[4],
-                            args[5], args[6], args[7]);
-    } else if (args.length === 9) {
-      ret = new constructor(args[0], args[1], args[2], args[3], args[4],
-                            args[5], args[6], args[7], args[8]);
-    } else if (args.length === 10) {
-      ret = new constructor(args[0], args[1], args[2], args[3], args[4],
-                            args[5], args[6], args[7], args[8], args[9]);
-    } else {
-      // Dummy Type with correct constructor.
-      var Type = function(){};
-      Type.prototype = constructor.prototype;
-  
-      // Create a new instance
-      var instance = new Type();
-  
-      // Call the original constructor.
-      ret = constructor.apply(instance, args);
-      ret = Object(ret) === ret ? ret : instance;
-    }
-    return serialize(ret);
-  }
-
-  // Remote handler to return the top-level JavaScript context.
-  function context(data) {
-    return serialize(globalContext);
-  }
-
-  // Remote handler to track number of live / allocated proxies.
-  function proxyCount() {
-    var live = proxiedObjectTable.count();
-    var total = proxiedObjectTable.total();
-    return [live, total];
-  }
-
-  // Return true if two JavaScript proxies are equal (==).
-  function proxyEquals(args) {
-    return deserialize(args[0]) == deserialize(args[1]);
-  }
-
-  // Return true if a JavaScript proxy is instance of a given type (instanceof).
-  function proxyInstanceof(args) {
-    var obj = unbind(deserialize(args[0]));
-    var type = unbind(deserialize(args[1]));
-    return obj instanceof type;
-  }
-
-  // Return true if a JavaScript proxy has a given property.
-  function proxyHasProperty(args) {
-    var obj = unbind(deserialize(args[0]));
-    var member = unbind(deserialize(args[1]));
-    return member in obj;
-  }
-
-  // Delete a given property of object.
-  function proxyDeleteProperty(args) {
-    var obj = unbind(deserialize(args[0]));
-    var member = unbind(deserialize(args[1]));
-    delete obj[member];
-  }
-
-  function proxyConvert(args) {
-    return serialize(deserializeDataTree(args));
-  }
-
-  function deserializeDataTree(data) {
-    var type = data[0];
-    var value = data[1];
-    if (type === 'map') {
-      var obj = {};
-      for (var i = 0; i < value.length; i++) {
-        obj[value[i][0]] = deserializeDataTree(value[i][1]);
-      }
-      return obj;
-    } else if (type === 'list') {
-      var list = [];
-      for (var i = 0; i < value.length; i++) {
-        list.push(deserializeDataTree(value[i]));
-      }
-      return list;
-    } else /* 'simple' */ {
-      return deserialize(value);
-    }
-  }
-
-  function makeGlobalPort(name, f) {
-    var port = new ReceivePortSync();
-    port.receive(f);
-    window.registerPort(name, port.toSendPort());
-  }
-
-  // Enters a new scope in the JavaScript context.
-  function enterJavaScriptScope() {
-    proxiedObjectTable.enterScope();
-  }
-
-  // Enters a new scope in both the JavaScript and Dart context.
-  var _dartEnterScopePort = null;
-  function enterScope() {
-    enterJavaScriptScope();
-    if (!_dartEnterScopePort) {
-      _dartEnterScopePort = window.lookupPort('js-dart-interop-enter-scope');
-    }
-    return _dartEnterScopePort.callSync([]);
-  }
-
-  // Exits the current scope (and invalidate local IDs) in the JavaScript
-  // context.
-  function exitJavaScriptScope() {
-    proxiedObjectTable.exitScope();
-  }
-
-  // Exits the current scope in both the JavaScript and Dart context.
-  var _dartExitScopePort = null;
-  function exitScope(depth) {
-    exitJavaScriptScope();
-    if (!_dartExitScopePort) {
-      _dartExitScopePort = window.lookupPort('js-dart-interop-exit-scope');
-    }
-    return _dartExitScopePort.callSync([ depth ]);
-  }
-
-  makeGlobalPort('dart-js-interop-context', context);
-  makeGlobalPort('dart-js-interop-create', construct);
-  makeGlobalPort('dart-js-interop-proxy-count', proxyCount);
-  makeGlobalPort('dart-js-interop-equals', proxyEquals);
-  makeGlobalPort('dart-js-interop-instanceof', proxyInstanceof);
-  makeGlobalPort('dart-js-interop-has-property', proxyHasProperty);
-  makeGlobalPort('dart-js-interop-delete-property', proxyDeleteProperty);
-  makeGlobalPort('dart-js-interop-convert', proxyConvert);
-  makeGlobalPort('dart-js-interop-enter-scope', enterJavaScriptScope);
-  makeGlobalPort('dart-js-interop-exit-scope', exitJavaScriptScope);
-  makeGlobalPort('dart-js-interop-globalize', function(data) {
-    if (data[0] == "objref" || data[0] == "funcref") return proxiedObjectTable.globalize(data[1]);
-    throw 'Illegal type: ' + data[0];
-  });
-  makeGlobalPort('dart-js-interop-invalidate', function(data) {
-    if (data[0] == "objref" || data[0] == "funcref") return proxiedObjectTable.invalidate(data[1]);
-    throw 'Illegal type: ' + data[0];
-  });
-})();
-""";
-
-// Injects JavaScript source code onto the page.
-// This is only used to load the bootstrapping code above.
-void _inject(code) {
-  final script = new ScriptElement();
-  script.type = 'text/javascript';
-  script.innerHtml = code;
-  document.body.nodes.add(script);
-}
-
-// Global ports to manage communication from Dart to JS.
-SendPortSync _jsPortSync = null;
-SendPortSync _jsPortCreate = null;
-SendPortSync _jsPortProxyCount = null;
-SendPortSync _jsPortEquals = null;
-SendPortSync _jsPortInstanceof = null;
-SendPortSync _jsPortHasProperty = null;
-SendPortSync _jsPortDeleteProperty = null;
-SendPortSync _jsPortConvert = null;
-SendPortSync _jsEnterJavaScriptScope = null;
-SendPortSync _jsExitJavaScriptScope = null;
-SendPortSync _jsGlobalize = null;
-SendPortSync _jsInvalidate = null;
-
-// Global ports to manage communication from JS to Dart.
-ReceivePortSync _dartEnterDartScope = null;
-ReceivePortSync _dartExitDartScope = null;
-
-// Initializes bootstrap code and ports.
-void _initialize() {
-  if (_jsPortSync != null) return;
-
-  // Test if the port is already defined.
-  try {
-    _jsPortSync = window.lookupPort('dart-js-interop-context');
-  } catch (e) {
-    // TODO(vsm): Suppress the exception until dartbug.com/5854 is fixed.
-  }
-
-  // If not, try injecting the script.
-  if (_jsPortSync == null) {
-    _inject(_JS_BOOTSTRAP);
-    _jsPortSync = window.lookupPort('dart-js-interop-context');
-  }
-
-  _jsPortCreate = window.lookupPort('dart-js-interop-create');
-  _jsPortProxyCount = window.lookupPort('dart-js-interop-proxy-count');
-  _jsPortEquals = window.lookupPort('dart-js-interop-equals');
-  _jsPortInstanceof = window.lookupPort('dart-js-interop-instanceof');
-  _jsPortHasProperty = window.lookupPort('dart-js-interop-has-property');
-  _jsPortDeleteProperty = window.lookupPort('dart-js-interop-delete-property');
-  _jsPortConvert = window.lookupPort('dart-js-interop-convert');
-  _jsEnterJavaScriptScope = window.lookupPort('dart-js-interop-enter-scope');
-  _jsExitJavaScriptScope = window.lookupPort('dart-js-interop-exit-scope');
-  _jsGlobalize = window.lookupPort('dart-js-interop-globalize');
-  _jsInvalidate = window.lookupPort('dart-js-interop-invalidate');
-
-  _dartEnterDartScope = new ReceivePortSync()
-    ..receive((_) => _enterScope());
-  _dartExitDartScope = new ReceivePortSync()
-    ..receive((args) => _exitScope(args[0]));
-  window.registerPort('js-dart-interop-enter-scope', _dartEnterDartScope.toSendPort());
-  window.registerPort('js-dart-interop-exit-scope', _dartExitDartScope.toSendPort());
-}
-
-/**
- * Returns a proxy to the global JavaScript context for this page.
- */
-Proxy get context {
-  _enterScopeIfNeeded();
-  return _deserialize(_jsPortSync.callSync([]));
-}
-
-// Depth of current scope.  Return 0 if no scope.
-get _depth => _proxiedObjectTable._scopeIndices.length;
-
-// If we are not already in a scope, enter one and register a
-// corresponding exit once we return to the event loop.
-void _enterScopeIfNeeded() {
-  if (_depth == 0) {
-    var depth = _enterScope();
-    scheduleMicrotask(() => _exitScope(depth));
-  }
-}
-
-/**
- * Executes the closure [f] within a scope.  Any proxies created within this
- * scope are invalidated afterward unless they are converted to a global proxy.
- */
-scoped(f) {
-  var depth = _enterScope();
-  try {
-    return f();
-  } finally {
-    _exitScope(depth);
-  }
-}
-
-int _enterScope() {
-  _initialize();
-  _proxiedObjectTable.enterScope();
-  _jsEnterJavaScriptScope.callSync([]);
-  return _proxiedObjectTable._scopeIndices.length;
-}
-
-void _exitScope(int depth) {
-  assert(_proxiedObjectTable._scopeIndices.length == depth);
-  _jsExitJavaScriptScope.callSync([]);
-  _proxiedObjectTable.exitScope();
-}
-
-/*
- * Enters a scope and returns the depth of the scope stack.
- */
-/// WARNING: This API is experimental and may be removed.
-int $experimentalEnterScope() {
-  return _enterScope();
-}
-
-/*
- * Exits a scope.  The [depth] must match that returned by the corresponding
- * enter scope call.
- */
-/// WARNING: This API is experimental and may be removed.
-void $experimentalExitScope(int depth) {
-  _exitScope(depth);
-}
-
-/**
- * Retains the given [object] beyond the current scope.
- * Instead, it will need to be explicitly released.
- * The given [object] is returned for convenience.
- */
-// TODO(aa) : change dynamic to Serializable<Proxy> if http://dartbug.com/9023
-// is fixed.
-// TODO(aa) : change to "<T extends Serializable<Proxy>> T retain(T object)"
-// once generic methods have landed.
-dynamic retain(Serializable<Proxy> object) {
-  _jsGlobalize.callSync(_serialize(object.toJs()));
-  return object;
-}
-
-/**
- * Releases a retained [object].
- */
-void release(Serializable<Proxy> object) {
-  _jsInvalidate.callSync(_serialize(object.toJs()));
-}
-
-/**
- * Check if [proxy] is instance of [type].
- */
-bool instanceof(Serializable<Proxy> proxy, Serializable<FunctionProxy> type) =>
-    _jsPortInstanceof.callSync([proxy.toJs(), type.toJs()].map(_serialize)
-        .toList());
-
-/**
- * Check if [proxy] has a [name] property.
- */
-bool hasProperty(Serializable<Proxy> proxy, String name) =>
-  _jsPortHasProperty.callSync([proxy.toJs(), name].map(_serialize).toList());
-
-/**
- * Delete the [name] property of [proxy].
- */
-void deleteProperty(Serializable<Proxy> proxy, String name) {
-  _jsPortDeleteProperty.callSync([proxy.toJs(), name].map(_serialize).toList());
-}
-
-/**
- * Converts a Dart map [data] to a JavaScript map and return a [Proxy] to it.
- */
-Proxy map(Map data) => new Proxy._json(data);
-
-/**
- * Converts a Dart [Iterable] to a JavaScript array and return a [Proxy] to it.
- */
-Proxy array(Iterable data) => new Proxy._json(data);
-
-/**
- * Converts a local Dart function to a callback that can be passed to
- * JavaScript.
- *
- * A callback can either be:
- *
- * - single-fire, in which case it is automatically invalidated after the first
- *   invocation, or
- * - multi-fire, in which case it must be explicitly disposed.
- */
-class Callback implements Serializable<FunctionProxy> {
-  var _manualDispose;
-  var _id;
-  var _callback;
-
-  _initialize(manualDispose) {
-    _manualDispose = manualDispose;
-    _id = _proxiedObjectTable.add(_callback);
-    _proxiedObjectTable.globalize(_id);
-  }
-
-  _dispose() {
-    var c = _proxiedObjectTable.invalidate(_id);
-  }
-
-  FunctionProxy toJs() =>
-      new FunctionProxy._internal(_proxiedObjectTable.sendPort, _id);
-
-  /**
-   * Disposes this [Callback] so that it may be collected.
-   * Once a [Callback] is disposed, it is an error to invoke it from JavaScript.
-   */
-  dispose() {
-    assert(_manualDispose);
-    _dispose();
-  }
-
-  /**
-   * Creates a single-fire [Callback] that invokes [f].  The callback is
-   * automatically disposed after the first invocation.
-   */
-  Callback.once(Function f, {bool withThis: false}) {
-    _callback = (List args) {
-      try {
-        return Function.apply(f, withThis ? args : args.skip(1).toList());
-      } finally {
-        _dispose();
-      }
-    };
-    _initialize(false);
-  }
-
-  /**
-   * Creates a multi-fire [Callback] that invokes [f].  The callback must be
-   * explicitly disposed to avoid memory leaks.
-   */
-  Callback.many(Function f, {bool withThis: false}) {
-    _callback = (List args) =>
-        Function.apply(f, withThis ? args : args.skip(1).toList());
-    _initialize(true);
-  }
-}
-
-// Detect unspecified arguments.
-class _Undefined {
-  const _Undefined();
-}
-const _undefined = const _Undefined();
-List _pruneUndefined(arg1, arg2, arg3, arg4, arg5, arg6) {
-  // This assumes no argument
-  final args = [arg1, arg2, arg3, arg4, arg5, arg6];
-  final index = args.indexOf(_undefined);
-  if (index < 0) return args;
-  return args.sublist(0, index);
-}
-
-/**
- * Proxies to JavaScript objects.
- */
-class Proxy implements Serializable<Proxy> {
-  SendPortSync _port;
-  final _id;
-
-  /**
-   * Constructs a [Proxy] to a new JavaScript object by invoking a (proxy to a)
-   * JavaScript [constructor].  The arguments should be either
-   * primitive values, DOM elements, or Proxies.
-   */
-  factory Proxy(Serializable<FunctionProxy> constructor,
-      [arg1 = _undefined,
-       arg2 = _undefined,
-       arg3 = _undefined,
-       arg4 = _undefined,
-       arg5 = _undefined,
-       arg6 = _undefined]) {
-      var arguments = _pruneUndefined(arg1, arg2, arg3, arg4, arg5, arg6);
-      return new Proxy.withArgList(constructor, arguments);
-  }
-
-  /**
-   * Constructs a [Proxy] to a new JavaScript object by invoking a (proxy to a)
-   * JavaScript [constructor].  The [arguments] list should contain either
-   * primitive values, DOM elements, or Proxies.
-   */
-  factory Proxy.withArgList(Serializable<FunctionProxy> constructor,
-      List arguments) {
-    _enterScopeIfNeeded();
-    final serialized = ([constructor]..addAll(arguments)).map(_serialize).
-        toList();
-    final result = _jsPortCreate.callSync(serialized);
-    return _deserialize(result);
-  }
-
-  /**
-   * Constructs a [Proxy] to a new JavaScript map or list created defined via
-   * Dart map or list.
-   */
-  factory Proxy._json(data) {
-    _enterScopeIfNeeded();
-    return _convert(data);
-  }
-
-  static _convert(data) {
-    return _deserialize(_jsPortConvert.callSync(_serializeDataTree(data)));
-  }
-
-  static _serializeDataTree(data) {
-    if (data is Map) {
-      final entries = new List();
-      for (var key in data.keys) {
-        entries.add([key, _serializeDataTree(data[key])]);
-      }
-      return ['map', entries];
-    } else if (data is Iterable) {
-      return ['list', data.map(_serializeDataTree).toList()];
-    } else {
-      return ['simple', _serialize(data)];
-    }
-  }
-
-  Proxy._internal(this._port, this._id);
-
-  Proxy toJs() => this;
-
-  // Resolve whether this is needed.
-  operator[](arg) => _forward(this, '[]', 'method', [ arg ]);
-
-  // Resolve whether this is needed.
-  operator[]=(key, value) => _forward(this, '[]=', 'method', [ key, value ]);
-
-  // Test if this is equivalent to another Proxy.  This essentially
-  // maps to JavaScript's == operator.
-  // TODO(vsm): Can we avoid forwarding to JS?
-  operator==(other) => identical(this, other)
-      ? true
-      : (other is Proxy &&
-         _jsPortEquals.callSync([_serialize(this), _serialize(other)]));
-
-  String toString() {
-    try {
-      return _forward(this, 'toString', 'method', []);
-    } catch(e) {
-      return super.toString();
-    }
-  }
-
-  // Forward member accesses to the backing JavaScript object.
-  noSuchMethod(Invocation invocation) {
-    String member = MirrorSystem.getName(invocation.memberName);
-    // If trying to access a JavaScript field/variable that starts with
-    // _ (underscore), Dart treats it a library private and member name
-    // it suffixed with '@internalLibraryIdentifier' which we have to
-    // strip before sending over to the JS side.
-    if (member.indexOf('@') != -1) {
-      member = member.substring(0, member.indexOf('@'));
-    }
-    String kind;
-    List args = invocation.positionalArguments;
-    if (args == null) args = [];
-    if (invocation.isGetter) {
-      kind = 'get';
-    } else if (invocation.isSetter) {
-      kind = 'set';
-      if (member.endsWith('=')) {
-        member = member.substring(0, member.length - 1);
-      }
-    } else if (member == 'call') {
-      // A 'call' (probably) means that this proxy was invoked directly
-      // as if it was a function.  Map this to JS function application.
-      kind = 'apply';
-    } else {
-      kind = 'method';
-    }
-    return _forward(this, member, kind, args);
-  }
-
-  // Forward member accesses to the backing JavaScript object.
-  static _forward(Proxy receiver, String member, String kind, List args) {
-    _enterScopeIfNeeded();
-    var result = receiver._port.callSync([receiver._id, member, kind,
-                                          args.map(_serialize).toList()]);
-    switch (result[0]) {
-      case 'return': return _deserialize(result[1]);
-      case 'throws': throw _deserialize(result[1]);
-      case 'none': throw new NoSuchMethodError(receiver, member, args, {});
-      default: throw 'Invalid return value';
-    }
-  }
-}
-
-// TODO(aa) make FunctionProxy implements Function once it is allowed
-/// A [Proxy] subtype to JavaScript functions.
-class FunctionProxy extends Proxy
-    implements Serializable<FunctionProxy> /*,Function*/ {
-  FunctionProxy._internal(SendPortSync port, id) : super._internal(port, id);
-
-  // TODO(vsm): This allows calls with a limited number of arguments
-  // in the context of dartbug.com/9283.  Eliminate pending the resolution
-  // of this bug.  Note, if this Proxy is called with more arguments then
-  // allowed below, it will trigger the 'call' path in Proxy.noSuchMethod
-  // - and still work correctly in unminified mode.
-  call([arg1 = _undefined, arg2 = _undefined,
-        arg3 = _undefined, arg4 = _undefined,
-        arg5 = _undefined, arg6 = _undefined]) {
-    var arguments = _pruneUndefined(arg1, arg2, arg3, arg4, arg5, arg6);
-    return Proxy._forward(this, '', 'apply', arguments);
-  }
-}
-
-/// Marker class used to indicate it is serializable to js. If a class is a
-/// [Serializable] the "toJs" method will be called and the result will be used
-/// as value.
-abstract class Serializable<T> {
-  T toJs();
-}
-
-// A table to managed local Dart objects that are proxied in JavaScript.
-class _ProxiedObjectTable {
-  // Debugging name.
-  final String _name;
-
-  // Generator for unique IDs.
-  int _nextId;
-
-  // Counter for invalidated IDs for debugging.
-  int _deletedCount;
-
-  // Table of IDs to Dart objects.
-  final Map<String, Object> _registry;
-
-  // Port to handle and forward requests to the underlying Dart objects.
-  // A remote proxy is uniquely identified by an ID and SendPortSync.
-  final ReceivePortSync _port;
-
-  // The set of IDs that are global.  These must be explicitly invalidated.
-  final Set<String> _globalIds;
-
-  // The stack of valid IDs.
-  final List<String> _handleStack;
-
-  // The stack of scopes, where each scope is represented by an index into the
-  // handleStack.
-  final List<int> _scopeIndices;
-
-  // Enters a new scope.
-  enterScope() {
-    _scopeIndices.add(_handleStack.length);
-  }
-
-  // Invalidates non-global IDs created in the current scope and
-  // restore to the previous scope.
-  exitScope() {
-    int start = _scopeIndices.removeLast();
-    for (int i = start; i < _handleStack.length; ++i) {
-      String key = _handleStack[i];
-      if (!_globalIds.contains(key)) {
-        _registry.remove(_handleStack[i]);
-        _deletedCount++;
-      }
-    }
-    if (start != _handleStack.length) {
-      _handleStack.removeRange(start, _handleStack.length - start);
-    }
-  }
-
-  // Converts an ID to a global.
-  globalize(id) => _globalIds.add(id);
-
-  // Invalidates an ID.
-  invalidate(id) {
-    var old = _registry[id];
-    _globalIds.remove(id);
-    _registry.remove(id);
-    _deletedCount++;
-    return old;
-  }
-
-  // Replaces the object referenced by an ID.
-  _replace(id, x) {
-    _registry[id] = x;
-  }
-
-  _ProxiedObjectTable() :
-      _name = 'dart-ref',
-      _nextId = 0,
-      _deletedCount = 0,
-      _registry = {},
-      _port = new ReceivePortSync(),
-      _handleStack = new List<String>(),
-      _scopeIndices = new List<int>(),
-      _globalIds = new Set<String>() {
-        _port.receive((msg) {
-          try {
-            final receiver = _registry[msg[0]];
-            final method = msg[1];
-            final args = msg[2].map(_deserialize).toList();
-            if (method == '#call') {
-              final func = receiver as Function;
-              var result = _serialize(func(args));
-              return ['return', result];
-            } else {
-              // TODO(vsm): Support a mechanism to register a handler here.
-              throw 'Invocation unsupported on non-function Dart proxies';
-            }
-          } catch (e) {
-            // TODO(vsm): callSync should just handle exceptions itself.
-            return ['throws', '$e'];
-          }
-        });
-      }
-
-  // Adds a new object to the table and return a new ID for it.
-  String add(x) {
-    _enterScopeIfNeeded();
-    // TODO(vsm): Cache x and reuse id.
-    final id = '$_name-${_nextId++}';
-    _registry[id] = x;
-    _handleStack.add(id);
-    return id;
-  }
-
-  // Gets an object by ID.
-  Object get(String id) {
-    return _registry[id];
-  }
-
-  // Gets the current number of objects kept alive by this table.
-  get count => _registry.length;
-
-  // Gets the total number of IDs ever allocated.
-  get total => count + _deletedCount;
-
-  // Gets a send port for this table.
-  get sendPort => _port.toSendPort();
-}
-
-// The singleton to manage proxied Dart objects.
-_ProxiedObjectTable _proxiedObjectTable = new _ProxiedObjectTable();
-
-/// End of proxy implementation.
-
-// Dart serialization support.
-
-_serialize(var message) {
-  if (message == null) {
-    return null;  // Convert undefined to null.
-  } else if (message is String ||
-             message is num ||
-             message is bool) {
-    // Primitives are passed directly through.
-    return message;
-  } else if (message is SendPortSync) {
-    // Non-proxied objects are serialized.
-    return message;
-  } else if (message is Element &&
-      (message.document == null || message.document == document)) {
-    return [ 'domref', _serializeElement(message) ];
-  } else if (message is FunctionProxy) {
-    // Remote function proxy.
-    return [ 'funcref', message._id, message._port ];
-  } else if (message is Proxy) {
-    // Remote object proxy.
-    return [ 'objref', message._id, message._port ];
-  } else if (message is Serializable) {
-    // use of result of toJs()
-    return _serialize(message.toJs());
-  } else {
-    // Local object proxy.
-    return [ 'objref',
-             _proxiedObjectTable.add(message),
-             _proxiedObjectTable.sendPort ];
-  }
-}
-
-_deserialize(var message) {
-  deserializeFunction(message) {
-    var id = message[1];
-    var port = message[2];
-    if (port == _proxiedObjectTable.sendPort) {
-      // Local function.
-      return _proxiedObjectTable.get(id);
-    } else {
-      // Remote function.  Forward to its port.
-      return new FunctionProxy._internal(port, id);
-    }
-  }
-
-  deserializeObject(message) {
-    var id = message[1];
-    var port = message[2];
-    if (port == _proxiedObjectTable.sendPort) {
-      // Local object.
-      return _proxiedObjectTable.get(id);
-    } else {
-      // Remote object.
-      return new Proxy._internal(port, id);
-    }
-  }
-
-
-  if (message == null) {
-    return null;  // Convert undefined to null.
-  } else if (message is String ||
-             message is num ||
-             message is bool) {
-    // Primitives are passed directly through.
-    return message;
-  } else if (message is SendPortSync) {
-    // Serialized type.
-    return message;
-  }
-  var tag = message[0];
-  switch (tag) {
-    case 'funcref': return deserializeFunction(message);
-    case 'objref': return deserializeObject(message);
-    case 'domref': return _deserializeElement(message[1]);
-  }
-  throw 'Unsupported serialized data: $message';
-}
-
-// DOM element serialization.
-
-int _localNextElementId = 0;
-
-const _DART_ID = 'data-dart_id';
-const _DART_TEMPORARY_ATTACHED = 'data-dart_temporary_attached';
-
-_serializeElement(Element e) {
-  // TODO(vsm): Use an isolate-specific id.
-  var id;
-  if (e.attributes.containsKey(_DART_ID)) {
-    id = e.attributes[_DART_ID];
-  } else {
-    id = 'dart-${_localNextElementId++}';
-    e.attributes[_DART_ID] = id;
-  }
-  if (!identical(e, document.documentElement)) {
-    // Element must be attached to DOM to be retrieve in js part.
-    // Attach top unattached parent to avoid detaching parent of "e" when
-    // appending "e" directly to document. We keep count of elements
-    // temporarily attached to prevent detaching top unattached parent to
-    // early. This count is equals to the length of _DART_TEMPORARY_ATTACHED
-    // attribute. There could be other elements to serialize having the same
-    // top unattached parent.
-    var top = e;
-    while (true) {
-      if (top.attributes.containsKey(_DART_TEMPORARY_ATTACHED)) {
-        final oldValue = top.attributes[_DART_TEMPORARY_ATTACHED];
-        final newValue = oldValue + 'a';
-        top.attributes[_DART_TEMPORARY_ATTACHED] = newValue;
-        break;
-      }
-      if (top.parent == null) {
-        top.attributes[_DART_TEMPORARY_ATTACHED] = 'a';
-        document.documentElement.children.add(top);
-        break;
-      }
-      if (identical(top.parent, document.documentElement)) {
-        // e was already attached to dom
-        break;
-      }
-      top = top.parent;
-    }
-  }
-  return id;
-}
-
-Element _deserializeElement(var id) {
-  var list = queryAll('[$_DART_ID="$id"]');
-  if (list.length > 1) throw 'Non unique ID: $id';
-  if (list.length == 0) {
-    throw 'Only elements attached to document can be serialized: $id';
-  }
-  final e = list[0];
-  if (!identical(e, document.documentElement)) {
-    // detach temporary attached element
-    var top = e;
-    while (true) {
-      if (top.attributes.containsKey(_DART_TEMPORARY_ATTACHED)) {
-        final oldValue = top.attributes[_DART_TEMPORARY_ATTACHED];
-        final newValue = oldValue.substring(1);
-        top.attributes[_DART_TEMPORARY_ATTACHED] = newValue;
-        // detach top only if no more elements have to be unserialized
-        if (top.attributes[_DART_TEMPORARY_ATTACHED].length == 0) {
-          top.attributes.remove(_DART_TEMPORARY_ATTACHED);
-          top.remove();
-        }
-        break;
-      }
-      if (identical(top.parent, document.documentElement)) {
-        // e was already attached to dom
-        break;
-      }
-      top = top.parent;
-    }
-  }
-  return e;
-}
-
-// Fetch the number of proxies to JavaScript objects.
-// This returns a 2 element list.  The first is the number of currently
-// live proxies.  The second is the total number of proxies ever
-// allocated.
-List _proxyCountJavaScript() => _jsPortProxyCount.callSync([]);
-
-/**
- * Returns the number of allocated proxy objects matching the given
- * conditions.  By default, the total number of live proxy objects are
- * return.  In a well behaved program, this should stay below a small
- * bound.
- *
- * Set [all] to true to return the total number of proxies ever allocated.
- * Set [dartOnly] to only count proxies to Dart objects (live or all).
- * Set [jsOnly] to only count proxies to JavaScript objects (live or all).
- */
-int proxyCount({all: false, dartOnly: false, jsOnly: false}) {
-  final js = !dartOnly;
-  final dart = !jsOnly;
-  final jsCounts = js ? _proxyCountJavaScript() : null;
-  var sum = 0;
-  if (!all) {
-    if (js)
-      sum += jsCounts[0];
-    if (dart)
-      sum += _proxiedObjectTable.count;
-  } else {
-    if (js)
-      sum += jsCounts[1];
-    if (dart)
-      sum += _proxiedObjectTable.total;
-  }
-  return sum;
-}
-
-// Prints the number of live handles in Dart and JavaScript.  This is for
-// debugging / profiling purposes.
-void _proxyDebug([String message = '']) {
-  print('Proxy status $message:');
-  var dartLive = proxyCount(dartOnly: true);
-  var dartTotal = proxyCount(dartOnly: true, all: true);
-  var jsLive = proxyCount(jsOnly: true);
-  var jsTotal = proxyCount(jsOnly: true, all: true);
-  print('  Dart objects Live : $dartLive (out of $dartTotal ever allocated).');
-  print('  JS objects Live : $jsLive (out of $jsTotal ever allocated).');
-}