Fix #13094. Pass index to .before(fn) fn as documented. Close gh-1093.

src/manipulation.js

@@ -286,16 +286,17 @@ jQuery.fn.extend({
 		var fragment, first, scripts, hasScripts, node, doc,
 			i = 0,
 			l = this.length,
+			set = this,
 			iNoClone = l - 1,
 			value = args[0],
 			isFunction = jQuery.isFunction( value );
 
 		// We can't cloneNode fragments that contain checked, in WebKit
 		if ( isFunction || !( l <= 1 || typeof value !== "string" || jQuery.support.checkClone || !rchecked.test( value ) ) ) {
-			return this.each(function() {
-				var self = jQuery( this );
+			return this.each(function( index ) {
+				var self = set.eq( index );
 				if ( isFunction ) {
-					args[0] = value.call( this, i, table ? self.html() : undefined );
+					args[0] = value.call( this, index, table ? self.html() : undefined );
 				}
 				self.domManip( args, table, callback );
 			});

test/unit/manipulation.js

@@ -2238,3 +2238,11 @@ test( "insertAfter, insertBefore, etc do not work when destination is original e
 		jQuery("#test4087-multiple").remove();
 	});
 });
+
+test( "Index for function argument should be received (#13094)", 2, function() {
+    var i = 0;
+
+    jQuery("<div/><div/>").before(function( index ) {
+        equal( index, i++, "Index should be correct" );
+    });
+});