diff --git a/src/MutationObserver/MutationObserver.js b/src/MutationObserver/MutationObserver.js
index be7dda9..833ac53 100644
--- a/src/MutationObserver/MutationObserver.js
+++ b/src/MutationObserver/MutationObserver.js
@@ -8,11 +8,30 @@
var registrationsTable = new WeakMap();
- // We use setImmediate or postMessage for our future callback.
- var setImmediate = window.msSetImmediate;
+ var setImmediate;
- // Use post message to emulate setImmediate.
- if (!setImmediate) {
+ // As much as we would like to use the native implementation, IE
+ // (all versions) suffers a rather annoying bug where it will drop or defer
+ // callbacks when heavy DOM operations are being performed concurrently.
+ //
+ // For a thorough discussion on this, see:
+ // http://codeforhire.com/2013/09/21/setimmediate-and-messagechannel-broken-on-internet-explorer-10/
+ if (/Trident/.test(navigator.userAgent)) {
+ // Sadly, this bug also affects postMessage and MessageQueues.
+ //
+ // We would like to use the onreadystatechange hack for IE <= 10, but it is
+ // dangerous in the polyfilled environment due to requiring that the
+ // observed script element be in the document.
+ setImmediate = setTimeout;
+
+ // If some other browser ever implements it, let's prefer their native
+ // implementation:
+ } else if (window.setImmediate) {
+ setImmediate = window.setImmediate;
+
+ // Otherwise, we fall back to postMessage as a means of emulating the next
+ // task semantics of setImmediate.
+ } else {
var setImmediateQueue = [];
var sentinel = String(Math.random());
window.addEventListener('message', function(e) {
diff --git a/src/ShadowDOM/microtask.js b/src/ShadowDOM/microtask.js
index c0e35b7..11ad4de 100644
--- a/src/ShadowDOM/microtask.js
+++ b/src/ShadowDOM/microtask.js
@@ -33,7 +33,7 @@
};
} else {
- timerFunc = window.setImmediate || window.setTimeout;
+ timerFunc = window.setTimeout;
}
function setEndOfMicrotask(func) {
diff --git a/workbench/ie10-task-flaking.html b/workbench/ie10-task-flaking.html
new file mode 100644
index 0000000..b723d2b
--- /dev/null
+++ b/workbench/ie10-task-flaking.html
@@ -0,0 +1,62 @@
+
+
+
+
+ MutationObserver
+
+
+
+
+
+
MutationObserver test page
+
+
Clicking start will schedule two self-restarting functions:
+
+
runSetTimeout uses setTimeout(fn, 0) for queueing itself
+
runMutation uses a MutationObserver for queueing itself
+
+
+
+After starting the test, move your mouse so that it is hovering over the top line of output.
+
+
+
+If the browser is behaving, you should see runSetTimeout calls interleaved with runMutation calls (either 2:1 or 1:1, depending).
+
+
+
+On IE10, if our MutationObserver polyfill uses setImmediate, postMessage, or MessageQueue, the runMutation line will become erratic, and eventually not fire at all.
+