dart:js - speed up constructor calls with few arguments.

sdk/lib/js/dart2js/js_dart2js.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.
 
 /**
  * Support for interoperating with JavaScript.
  *
  * This library provides access to JavaScript objects from Dart, allowing
  * Dart code to get and set properties, and call methods of JavaScript objects
  * and invoke JavaScript functions. The library takes care of converting
@@ skipping 123 matching lines @@
 
   /**
    * Constructs a new JavaScript object from [constructor] and returns a proxy
    * to it.
    */
   factory JsObject(JsFunction constructor, [List arguments]) {
     var constr = _convertToJS(constructor);
     if (arguments == null) {
       return _wrapToDart(JS('', 'new #()', constr));
     }
+
+    if (JS('bool', '# instanceof Array', arguments)) {
+      int argumentCount = JS('int', '#.length', arguments);
+      switch (argumentCount) {
+        case 0:
+          return _wrapToDart(JS('', 'new #()', constr));
+
+        case 1:
+          var arg0 = _convertToJS(JS('', '#[0]', arguments));
+          return _wrapToDart(JS('', 'new #(#)', constr, arg0));
+
+        case 2:
+          var arg0 = _convertToJS(JS('', '#[0]', arguments));
+          var arg1 = _convertToJS(JS('', '#[1]', arguments));
+          return _wrapToDart(JS('', 'new #(#, #)', constr, arg0, arg1));

[Siggi Cherem (dart-lang), 2015/05/26 16:35:18]

any reason why not write these 3 lines as:
return _wrapToDArt(JS('',
    'new #(#[0], #[1])',
    constr, arguments, arguments));

or use a named template 'new #ctor(#argumets[0], #arguments[1])' ?

[sra1, 2015/05/26 17:58:58]

Not really, but the expression gets big and any automatic layout will either
make it ugly or make it take a lot of lines.
I like this but named template parameters are not available to the JS 'function'
since the arguments are decomposed/spread at compile time.

+
+        case 3:
+          var arg0 = _convertToJS(JS('', '#[0]', arguments));
+          var arg1 = _convertToJS(JS('', '#[1]', arguments));
+          var arg2 = _convertToJS(JS('', '#[2]', arguments));
+          return _wrapToDart(JS('', 'new #(#, #, #)', constr, arg0, arg1, arg2));

[Siggi Cherem (dart-lang), 2015/05/26 16:35:18]

wrap

[sra1, 2015/05/26 17:58:59]

Done.

+
+        case 4:
+          var arg0 = _convertToJS(JS('', '#[0]', arguments));
+          var arg1 = _convertToJS(JS('', '#[1]', arguments));
+          var arg2 = _convertToJS(JS('', '#[2]', arguments));
+          var arg3 = _convertToJS(JS('', '#[3]', arguments));
+          return _wrapToDart(
+              JS('', 'new #(#, #, #, #)', constr, arg0, arg1, arg2, arg3));
+      }
+    }
+
     // The following code solves the problem of invoking a JavaScript
     // constructor with an unknown number arguments.
     // First bind the constructor to the argument list using bind.apply().
     // The first argument to bind() is the binding of 'this', so add 'null' to
     // the arguments list passed to apply().
     // After that, use the JavaScript 'new' operator which overrides any binding
     // of 'this' with the new instance.
     var args = [null]..addAll(arguments.map(_convertToJS));
     var factoryFunction = JS('', '#.bind.apply(#, #)', constr, constr, args);
     // Without this line, calling factoryFunction as a constructor throws
     JS('String', 'String(#)', factoryFunction);
     // This could return an UnknownJavaScriptObject, or a native
     // object for which there is an interceptor
-    var jsObj = JS('JavaScriptObject', 'new #()', factoryFunction);

[Siggi Cherem (dart-lang), 2015/05/26 16:35:18]

I'm not familiar with this annotation here - any reason to remove it at this
point? Or is it equivalent to not provide anything in the first arg?

[sra1, 2015/05/26 17:58:58]

The constructor could be a constructor for something understood by Dart, e.g
Blob or typed array.

+    var jsObj = JS('', 'new #()', factoryFunction);
 
     return _wrapToDart(jsObj);
+
+    // TODO(sra): Investigate:
+    //
+    //     var jsObj = JS('', 'Object.create(#.prototype)', constr);
+    //     JS('', '#.apply(#, #)', constr, jsObj,
+    //         []..addAll(arguments.map(_convertToJS)));
+    //     return _wrapToDart(jsObj);
   }
 
   /**
    * Constructs a [JsObject] that proxies a native Dart object; _for expert use
    * only_.
    *
    * Use this constructor only if you wish to get access to JavaScript
    * properties attached to a browser host object, such as a Node or Blob, that
    * is normally automatically converted into a native Dart object.
    *
@@ skipping 333 matching lines @@
 
 // The shared constructor function for proxies to Dart objects in JavaScript.
 final _dartProxyCtor = JS('', 'function DartObject(o) { this.o = o; }');
 
 dynamic _convertToJS(dynamic o) {
   // Note: we don't write `if (o == null) return null;` to make sure dart2js
   // doesn't convert `return null;` into `return;` (which would make `null` be
   // `undefined` in Javascprit). See dartbug.com/20305 for details.
   if (o == null || o is String || o is num || o is bool) {
     return o;
-  } else if (o is Blob || o is Event || o is KeyRange || o is ImageData
-      || o is Node || o is TypedData || o is Window) {
+  }
+  if (o is JsObject) {

[Siggi Cherem (dart-lang), 2015/05/26 16:35:18]

just to make sure I'm not missing something, these changes in this function are
just style, right?

[sra1, 2015/05/26 17:58:59]

Yes.  Initially I had just moved || to the end of the line.

+    return o._jsObject;
+  }
+  if (o is Blob || o is Event || o is KeyRange || o is ImageData || o is Node ||
+      o is TypedData || o is Window) {
     return o;
-  } else if (o is DateTime) {
+  }
+  if (o is DateTime) {
     return Primitives.lazyAsJsDate(o);
-  } else if (o is JsObject) {
-    return o._jsObject;
-  } else if (o is Function) {
+  }
+  if (o is Function) {
     return _getJsProxy(o, _JS_FUNCTION_PROPERTY_NAME, (o) {
       var jsFunction = _convertDartFunction(o);
       // set a property on the JS closure referencing the Dart closure
       _defineProperty(jsFunction, _DART_CLOSURE_PROPERTY_NAME, o);
       return jsFunction;
     });
-  } else {
-    var ctor = _dartProxyCtor;
-    return _getJsProxy(o, _JS_OBJECT_PROPERTY_NAME,
-        (o) => JS('', 'new #(#)', ctor, o));
   }
+  var ctor = _dartProxyCtor;
+  return _getJsProxy(o, _JS_OBJECT_PROPERTY_NAME,
+      (o) => JS('', 'new #(#)', ctor, o));
 }
 
 Object _getJsProxy(o, String propertyName, createProxy(o)) {
   var jsProxy = _getOwnProperty(o, propertyName);
   if (jsProxy == null) {
     jsProxy = createProxy(o);
     _defineProperty(o, propertyName, jsProxy);
   }
   return jsProxy;
 }
@@ skipping 18 matching lines @@
     return JS('', '#.o', o);
   } else {
     return _wrapToDart(o);
   }
 }
 
 JsObject _wrapToDart(o) {
   if (JS('bool', 'typeof # == "function"', o)) {
     return _getDartProxy(o, _DART_CLOSURE_PROPERTY_NAME,
         (o) => new JsFunction._fromJs(o));
-  } else if (JS('bool', '# instanceof Array', o)) {
+  }
+  if (JS('bool', '# instanceof Array', o)) {
     return _getDartProxy(o, _DART_OBJECT_PROPERTY_NAME,
         (o) => new JsArray._fromJs(o));
-  } else {
-    return _getDartProxy(o, _DART_OBJECT_PROPERTY_NAME,
-        (o) => new JsObject._fromJs(o));
   }
+  return _getDartProxy(o, _DART_OBJECT_PROPERTY_NAME,
+      (o) => new JsObject._fromJs(o));
 }
 
 Object _getDartProxy(o, String propertyName, createProxy(o)) {
   var dartProxy = _getOwnProperty(o, propertyName);
   // Temporary fix for dartbug.com/15193
   // In some cases it's possible to see a JavaScript object that
   // came from a different context and was previously proxied to
   // Dart in that context. The JS object will have a cached proxy
   // but it won't be a valid Dart object in this context.
   // For now we throw away the cached proxy, but we should be able
   // to cache proxies from multiple JS contexts and Dart isolates.
   if (dartProxy == null || !_isLocalObject(o)) {
     dartProxy = createProxy(o);
     _defineProperty(o, propertyName, dartProxy);
   }
   return dartProxy;
 }