Page rollback to the top js

[Html] <script language = "javascript"> var goto_top_type =-1; var goto_top_itv = 0; function goto_top_timer () {var y = goto_top_type = 1? Document.doc umentElement. scrollTop: document. body. scrollTop; var moveby = 15; y-= Math. ceil (y * moveby/100); if (y <0) {y = 0;} if (goto_top_type = 1) {document.doc umentElement. scrollTop = y;} else {document. body. scrollTop = y;} if (y = 0) {clearInterval (goto_top_itv); goto_top_itv = 0 ;}} function goto_top () {if (goto_top_itv = 0) {www.2cto.com if (document.doc umentElement & document.doc umentElement. scrollTop) {goto_top_type = 1;} else if (document. body & document. body. scrollTop) {goto_top_type = 2;} else {goto_top_type = 0;} if (goto_top_type> 0) {goto_top_itv = setInterval ('Goto _ top_timer () ', 50 );}}} </script> <a href = "javascript: void (0)" onclick = "goto_top ()"> [Back to Top] </a>