perf(jqLite): don't recreate the Node.contains polyfill

Author: IgorMinar

src/jqLite.js

@@ -156,6 +156,30 @@ wrapMap.optgroup = wrapMap.option;
 wrapMap.tbody = wrapMap.tfoot = wrapMap.colgroup = wrapMap.caption = wrapMap.thead;
 wrapMap.th = wrapMap.td;
 
+
+var elementContains = document.head.contains ||
+      document.head.compareDocumentPosition
+        ? function( a, b ) {
+          // jshint bitwise: false
+          var adown = a.nodeType === 9 ? a.documentElement : a,
+              bup = b && b.parentNode;
+          return a === bup || !!( bup && bup.nodeType === 1 && (
+              adown.contains ?
+                  adown.contains( bup ) :
+                  a.compareDocumentPosition && a.compareDocumentPosition( bup ) & 16
+              ));
+          }
+        : function( a, b ) {
+            if ( b ) {
+              while ( (b = b.parentNode) ) {
+                if ( b === a ) {
+                  return true;
+                }
+              }
+            }
+            return false;
+          };
+
 function jqLiteIsTextNode(html) {
   return !HTML_REGEXP.test(html);
 }
@@ -782,28 +806,6 @@ forEach({
 
       if (!eventFns) {
         if (type == 'mouseenter' || type == 'mouseleave') {
-          var contains = document.body.contains || document.body.compareDocumentPosition ?
-          function( a, b ) {
-            // jshint bitwise: false
-            var adown = a.nodeType === 9 ? a.documentElement : a,
-            bup = b && b.parentNode;
-            return a === bup || !!( bup && bup.nodeType === 1 && (
-              adown.contains ?
-              adown.contains( bup ) :
-              a.compareDocumentPosition && a.compareDocumentPosition( bup ) & 16
-              ));
-            } :
-            function( a, b ) {
-              if ( b ) {
-                while ( (b = b.parentNode) ) {
-                  if ( b === a ) {
-                    return true;
-                  }
-                }
-              }
-              return false;
-            };
-
           events[type] = [];
 
           // Refer to jQuery's implementation of mouseenter & mouseleave
@@ -815,7 +817,7 @@ forEach({
             var target = this, related = event.relatedTarget;
             // For mousenter/leave call the handler if related is outside the target.
             // NB: No relatedTarget if the mouse left/entered the browser window
-            if ( !related || (related !== target && !contains(target, related)) ){
+            if ( !related || (related !== target && !elementContains(target, related)) ){
               handle(event, type);
             }
           });