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 2077 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) {
+  Isolate.\$isolateProperties.\$currentScript = currentScript;

[ahe, 2013/08/12 15:58:39]

Did you test this in minified mode? I think it needs to be:

'${namer.isolateName}.${namer.isolatePropertiesName}.\$currentScript =
currentScript;

Test it using:

test.py -mrelease -cdart2js -rdrt --minified

[blois, 2013/08/12 17:00:07]

Fixed, thanks!

+
+  if (typeof console !== 'undefined' && typeof document !== 'undefined' &&
+      document.readyState == "loading") {
+    // Bug dartbug.com/12281 this warning is to let users know how to match

[ahe, 2013/08/12 15:58:39]

I think you can avoid including this comment in the generated JS code by using
this trick:

      document.readyState == "loading") {'''
    // Bug dartbug.com/12281 this warning is to let users know how to match
    // Dartium execution timing.
'''

[blois, 2013/08/12 17:00:07]

I wanted this comment in the file for the near term so devs would have a
reference for more information. The bug is for removing the warning and this
comment.

[ahe, 2013/08/12 17:08:01]

If you want devs to read this message, shouldn't it be part of the warning?

How about:

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.");

[blois, 2013/08/12 17:43:46]

Fixed. I was figuring that the code comment was sufficient since the dev needs
to have the console open in the first place, but not really necessary since the
comment is small enough.

+    // Dartium execution timing.
+    console.warn("Dart script executed synchronously, use <script src='" +

[ahe, 2013/08/12 15:58:39]

Does this work on IE? I have heard that the console object doesn't exist when
the error console window isn't open in IE.

[blois, 2013/08/12 17:00:07]

Console isn't defined on FF in this case either- there's a check for console
above this block.

Tested on IE9, IE10, IE11 & FF.

[ahe, 2013/08/12 17:08:01]

Doh!

+        currentScript.src + "' defer></scr" + "ipt> to execute after parsing " +
+        "has completed.");
+  }
   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].
 """;