常用JavaScript操作页面元素的方法

 var ddl =document.getElementById(‘<%=ddlusers.ClientID%>‘);
        var index = ddl.selectedIndex;
        var Value = ddl.options[index].value;
        var Text = ddl.options[index].text;

  document.getElementById(‘<%=txtzfry.ClientID%>‘).value = str2;

  var aa = document.getElementsByName("box");
            var v = "";
            var title = "";
            for (var i = 0; i < aa.length; i++) {
                if (aa[i].checked) {
                    v += aa[i].value + ",";
                    title += aa[i].title + ",";
                    
                }
            } 

 function qiehuan(v) {
            if (v == "1") {
                $("#btn1").show();
                $("#btn2").hide();

            } else {
                $("#btn2").show();
                $("#btn1").hide();

            }
           }

 <span id="btn1">
    <input name="btnReturn" type="button" value="打印表单" class="btn yellow" onclick="javascript:prn1_preview()" />
          </span>
        <span id="btn2" style="display:none;">
    <input name="btnReturn2" type="button" value="打印表单" class="btn yellow" onclick="javascript:prn2_preview()" />
          </span>

title.substring(0, title.length - 1);