function PartialClient() {
            //Do stuff...
            var partialName = document.Form2.txtClientPartial.value;
            var c = document.Form2.ddlVendors;
            if (partialName != "") {
                for (var i = 0; i < c.length; i++) {
                    if (c[i].text.toUpperCase().indexOf(partialName.toUpperCase()) == 0)  {
                        //document.Form2.attrib_1.selectedIndex = i;
                        document.Form2.ddlVendors.selectedIndex = i;
                        break;
                    }
                   else if (c[i].value == partialName.toUpperCase()){
                        document.Form2.ddlVendors.selectedIndex = i;
                        break;
                    }
                   
                }
            }

type ahead textbox to dropdown

javascript, html

JavaScript