Tightening up dart2js load timing.

sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart

 // Copyright (c) 2012, 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.
 
 part of js_backend;
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
@@ skipping 839 matching lines @@
     if (needsDefineClass) {
       copyFinishClasses.add(
           js('newIsolate.$finishClassesProperty = '
              '    oldIsolate.$finishClassesProperty'));
     }
 
     // function(oldIsolate) {
     return js.fun('oldIsolate', [
       js('var isolateProperties = oldIsolate.${namer.isolatePropertiesName}'),
 
-      js(r'isolateProperties.$currentScript ='
-              'typeof document == "object" ?'
-              '(document.currentScript ||'
-                     'document.scripts[document.scripts.length - 1]) :'
-              'null'),
+      js(r'isolateProperties.$currentScript = null'),
 
       js('var isolatePrototype = oldIsolate.prototype'),
       js('var str = "{\\n"'),
       js('str += "var properties = '
                      'arguments.callee.${namer.isolatePropertiesName};\\n"'),
       js('var hasOwnProperty = Object.prototype.hasOwnProperty'),
 
       // for (var staticName in isolateProperties) {
       js.forIn('staticName', 'isolateProperties', [
         js.if_('hasOwnProperty.call(isolateProperties, staticName)', [
@@ skipping 2080 matching lines @@
     } else {
       mainCall = '${namer.isolateAccess(main)}()';
     }
     if (backend.needToInitializeDispatchProperty) {
       buffer.write(
           jsAst.prettyPrint(generateDispatchPropertyInitialization(),
                             compiler));
       buffer.write(N);
     }
     addComment('BEGIN invoke [main].', buffer);
+    // This code finds the currently executing script by listening to the
+    // onload event of all script tags and getting the first script which
+    // finishes. Since onload is called immediately after execution this should
+    // not substantially change execution order.
     buffer.write("""
-if (typeof document !== "undefined" && document.readyState !== "complete") {
-  document.addEventListener("readystatechange", function () {
-    if (document.readyState == "complete") {
-      if (typeof dartMainRunner === "function") {
-        dartMainRunner(function() { ${mainCall}; });
-      } else {
-        ${mainCall};
-      }
+;(function (callback) {
+  if (typeof document === 'undefined') {
+    callback(null);
+    return;
+  }
+  if (document.currentScript) {
+    callback(document.currentScript);
+    return;
+  }
+
+  var scripts = document.scripts;
+  function onLoad() {
+    for (var i = 0; i < scripts.length; ++i) {
+      scripts[i].removeEventListener('load', onLoad, false);
     }
-  }, false);
-} else {
+    callback(event.target);
+  }
+  for (var i = 0; i < scripts.length; ++i) {
+    scripts[i].addEventListener('load', onLoad, false);
+  }
+})(function(currentScript) {
+  ${namer.isolateName}.${namer.isolatePropertiesName}.\$currentScript =
+      currentScript;
+
+  if (typeof console !== 'undefined' && typeof document !== 'undefined' &&
+      document.readyState == "loading") {
+    console.warn("Dart script executed synchronously, use <script src='" +
+        currentScript.src + "' defer></scr" + "ipt> to execute after parsing " +
+        "has completed. See also http://dartbug.com/12281.");
+  }
   if (typeof dartMainRunner === "function") {
     dartMainRunner(function() { ${mainCall}; });
   } else {
     ${mainCall};
   }
-}
+});
 """);
     addComment('END invoke [main].', buffer);
   }
 
   void emitGetInterceptorMethod(CodeBuffer buffer,
                                 String key,
                                 Iterable<ClassElement> classes) {
     jsAst.Statement buildReturnInterceptor(ClassElement cls) {
       return js.return_(js(namer.isolateAccess(cls))['prototype']);
     }
@@ skipping 1071 matching lines @@
 
 const String HOOKS_API_USAGE = """
 // The code supports the following hooks:
 // dartPrint(message)   - if this function is defined it is called
 //                        instead of the Dart [print] method.
 // dartMainRunner(main) - if this function is defined, the Dart [main]
 //                        method will not be invoked directly.
 //                        Instead, a closure that will invoke [main] is
 //                        passed to [dartMainRunner].
 """;