Selector: Use shallow equality to compare documents to avoid IE/Edge …

…crashes

IE/Edge sometimes crash when comparing documents between frames using the strict
equality operator (`===` & `!==`). Funnily enough, shallow comparisons
(`==` & `!=`) work without crashing.

Fixes jquerygh-4441

src/selector.js

@@ -173,7 +173,11 @@ function find( selector, context, results, seed ) {
 	// Try to shortcut find operations (as opposed to filters) in HTML documents
 	if ( !seed ) {
 
-		if ( ( context ? context.ownerDocument || context : preferredDoc ) !== document ) {
+		// Support: IE 11+, Edge 17 - 18+
+		// IE/Edge sometimes throw a "Permission denied" error when strict-comparing
+		// two documents; shallow comparisons work.
+		// eslint-disable-next-line eqeqeq
+		if ( ( context ? context.ownerDocument || context : preferredDoc ) != document ) {
 			setDocument( context );
 		}
 		context = context || document;
@@ -425,7 +429,11 @@ function setDocument( node ) {
 		doc = node ? node.ownerDocument || node : preferredDoc;
 
 	// Return early if doc is invalid or already selected
-	if ( doc === document || doc.nodeType !== 9 ) {
+	// Support: IE 11+, Edge 17 - 18+
+	// IE/Edge sometimes throw a "Permission denied" error when strict-comparing
+	// two documents; shallow comparisons work.
+	// eslint-disable-next-line eqeqeq
+	if ( doc == document || doc.nodeType !== 9 ) {
 		return;
 	}
 
@@ -436,7 +444,11 @@ function setDocument( node ) {
 
 	// Support: IE 9 - 11+, Edge 12 - 18+
 	// Accessing iframe documents after unload throws "permission denied" errors (jQuery #13936)
-	if ( preferredDoc !== document &&
+	// Support: IE 11+, Edge 17 - 18+
+	// IE/Edge sometimes throw a "Permission denied" error when strict-comparing
+	// two documents; shallow comparisons work.
+	// eslint-disable-next-line eqeqeq
+	if ( preferredDoc != document &&
 		( subWindow = document.defaultView ) && subWindow.top !== subWindow ) {
 
 		// Support: IE 9 - 11+, Edge 12 - 18+
@@ -451,7 +463,11 @@ find.matches = function( expr, elements ) {
 find.matchesSelector = function( elem, expr ) {
 
 	// Set document vars if needed
-	if ( ( elem.ownerDocument || elem ) !== document ) {
+	// Support: IE 11+, Edge 17 - 18+
+	// IE/Edge sometimes throw a "Permission denied" error when strict-comparing
+	// two documents; shallow comparisons work.
+	// eslint-disable-next-line eqeqeq
+	if ( ( elem.ownerDocument || elem ) != document ) {
 		setDocument( elem );
 	}
 
@@ -1413,14 +1429,24 @@ function matcherFromGroupMatchers( elementMatchers, setMatchers ) {
 				dirrunsUnique = ( dirruns += contextBackup == null ? 1 : Math.random() || 0.1 );
 
 			if ( outermost ) {
-				outermostContext = context === document || context || outermost;
+
+				// Support: IE 11+, Edge 17 - 18+
+				// IE/Edge sometimes throw a "Permission denied" error when strict-comparing
+				// two documents; shallow comparisons work.
+				// eslint-disable-next-line eqeqeq
+				outermostContext = context == document || context || outermost;
 			}
 
 			// Add elements passing elementMatchers directly to results
 			for ( ; ( elem = elems[ i ] ) != null; i++ ) {
 				if ( byElement && elem ) {
 					j = 0;
-					if ( !context && elem.ownerDocument !== document ) {
+
+					// Support: IE 11+, Edge 17 - 18+
+					// IE/Edge sometimes throw a "Permission denied" error when strict-comparing
+					// two documents; shallow comparisons work.
+					// eslint-disable-next-line eqeqeq
+					if ( !context && elem.ownerDocument != document ) {
 						setDocument( elem );
 						xml = !documentIsHTML;
 					}