Tightening up dart2js load timing.

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

Index: sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart b/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
index 7c07ce10eb507bdd475166689632ead7479b03a7..caf74942cbba22da858d4009ba26be24867e062e 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
@@ -857,11 +857,7 @@ class CodeEmitterTask extends CompilerTask {
     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"'),
@@ -2959,24 +2955,48 @@ class CodeEmitterTask extends CompilerTask {
       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);
   }