Rewrote .offsetParent() to work against the full jQuery set, added tests. Fixes #4922.

src/offset.js

@@ -147,11 +147,13 @@ jQuery.fn.extend({
 	},
 
 	offsetParent: function() {
-		var offsetParent = this[0].offsetParent || document.body;
-		while ( offsetParent && (!/^body|html$/i.test(offsetParent.tagName) && jQuery.css(offsetParent, 'position') === 'static') ) {
-			offsetParent = offsetParent.offsetParent;
-		}
-		return jQuery( offsetParent );
+		return this.map(function(){
+			var offsetParent = this.offsetParent || document.body;
+			while ( offsetParent && (!/^body|html$/i.test(offsetParent.tagName) && jQuery.css(offsetParent, 'position') === 'static') ) {
+				offsetParent = offsetParent.offsetParent;
+			}
+			return offsetParent;
+		});
 	}
 });
 

test/unit/offset.js

@@ -145,7 +145,32 @@ testoffset("body", function( jQuery ) {
 	equals( jQuery('body').offset().left, 1, "jQuery('#body').offset().left" );
 });
 
+test("offsetParent", function(){
+	expect(11);
 
+	var body = jQuery("body").offsetParent();
+	equals( body.length, 1, "Only one offsetParent found." );
+	equals( body[0], document.body, "The body is its own offsetParent." );
+
+	var header = jQuery("#header").offsetParent();
+	equals( header.length, 1, "Only one offsetParent found." );
+	equals( header[0], document.body, "The body is the offsetParent." );
+
+	var div = jQuery("#nothiddendivchild").offsetParent();
+	equals( div.length, 1, "Only one offsetParent found." );
+	equals( div[0], document.body, "The body is the offsetParent." );
+
+	jQuery("#nothiddendiv").css("position", "relative");
+
+	div = jQuery("#nothiddendivchild").offsetParent();
+	equals( div.length, 1, "Only one offsetParent found." );
+	equals( div[0], jQuery("#nothiddendiv")[0], "The div is the offsetParent." );
+
+	div = jQuery("body, #nothiddendivchild").offsetParent();
+	equals( div.length, 2, "Two offsetParent found." );
+	equals( div[0], document.body, "The body is the offsetParent." );
+	equals( div[1], jQuery("#nothiddendiv")[0], "The div is the offsetParent." );
+});
 
 function testoffset(name, fn) {
 	
@@ -177,4 +202,4 @@ function testoffset(name, fn) {
 		iframe.contentWindow.location = src;
 		return iframe;
 	}
-}
+}
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