select标签，通过代码设置选中项

Select
清空原选择项：
document.getElementById("select_zjlx")[1].selected = false;
document.getElementById("select_zjlx")[2].selected = false;
document.getElementById("select_zjlx")[3].selected = false;
document.getElementById("select_zjlx")[4].selected = false;
设置新选择项
document.getElementById("select_zjlx")[0].selected = true;
document.getElementById("sfzh").value = "";
document.getElementById("xm").value = "";

附注：html中<select>标签用法解析http://www.169it.com/article/381029070941313083.html

使用实例：

一、html

1、

    <select id="select_zjlx" class="selectbox1" onchange="change(this)">
            <option value="R" selected="selected">中国大陆居民</option>
            <option value="H" >香港居民</option>
            <option value="M" >澳门居民</option>
            <option value="T" >台湾居民</option>
            <option value="F" >外国人</option>
    </select>

2、

<div class="china" >
    <div class="tj_cell">
        <div class="tj_cell_ft" style="width:80px">身份证号</div>
        <div class="tj_cell_primary">
            <input id="sfzh" class="tj_input" type="text" maxlength="18" placeholder="请输入身份证号" />
        </div>
    </div>
    <div class="tj_cell">
        <div class="tj_cell_ft" style="width:80px">姓&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;名</div>
        <div class="tj_cell_primary">
            <input id="xm" class="tj_input" type="text" maxlength="9" placeholder="请输入姓名（简体）" />
        </div>
    </div>
</div>
<div class="foreign" style="display:none;">
    <div class="tj_cell">
        <div class="tj_cell_ft" style="width:80px">国籍地区</div>
        <div class="tj_cell_primary">
            <select id="select_gjdq" class="selectbox1" onchange="change(this)">
                @{
                    System.Data.DataTable dt_Source = ViewBag.dt_Source;
                    if (dt_Source.Rows.Count == 0)
                    {

                    }
                    else
                    {
                        foreach (System.Data.DataRow row in dt_Source.Rows)
                        {
                            <option value=@row["DM"]>@row["MC"]</option>
                        }
                    }
                }
                
            </select>
        </div>
    </div>
    <div class="tj_cell">
        <div class="tj_cell_ft" style="width:80px">证件种类</div>
        <div class="tj_cell_primary">
            <select id="select_zjzl" class="selectbox1" onchange="">
                <option value="14" selected="selected">普通护照</option>
                <option value="13">因公普通护照</option>
                <option value="11">公务护照</option>
                <option value="12">外交护照</option>
            </select>
        </div>
    </div>
    <div class="tj_cell">
        <div class="tj_cell_ft" style="width:80px">证件号码</div>
        <div class="tj_cell_primary">
            <input id="zjhm" class="tj_input" type="text" maxlength="18" placeholder="请输入证件号码" />
        </div>
    </div>

二、script

1、

 function change(o) {
        var rylb = o.value;
        var sfzh = document.getElementById("sfzh");
        switch (rylb) {
            case "R":
                chinashow();
                foreignhide();
                sfzh.placeholder = "请输入身份证号";
               
                break;

            case "H":
                chinashow();
                foreignhide();
                sfzh.placeholder = "请输入香港身份证号";
                break;

            case "M":
                chinashow();
                foreignhide();
                sfzh.placeholder = "请输入澳门身份证号";
                break;

            case "T":
                chinashow();
                foreignhide();
                sfzh.placeholder = "请输入台湾身份证号";
                break;

            case "F":
                chinahide();
                foreignshow();
                break;

            default:

        }
    }

2、

 function SearchProgress() {
        // 查询结果，隐藏+置空
        $("#lbRsultValue").hide();
        $("#lrv").html('');

        var sfzh = $("#sfzh").val();
        var xm = $("#xm").val();
        var rylb = $("#select_zjlx").val();
        var gjdq = $("#select_gjdq").val();
        var zjzl = $("#select_zjzl").val();
        var zjhm = $("#zjhm").val();
        if (rylb != "F") {
            // 验证身份证号是否存在
            if (!sfzhvalidate("sfzh")) {
                return false;
            }
            // 姓名是否填写
            if (xm == null) {
                alert("请填写姓名");
                return;
            }
        } 
      

        if (rylb == "F") {
            // 外国人
            $("#zjhm").val(zjhm.toUpperCase());
            zjhm = zjhm.toUpperCase();
            AjaxSubmit('@Url.Action("ForeignJDCX", "YWCX")', {rylb:rylb, gjdq:gjdq, zjzl:zjzl, zjhm:zjhm }, null, function (data) {

                if (data.Result && data.Data != null) {
                    
                    RestoreState();                        
                    location.href = "@Url.Action("WJSLBHCXJG", "YWCX")?rylb=" + rylb + "&gjdq=" + gjdq + "&zjzl=" + zjzl + "&zjhm=" + zjhm + "&type=2";
                                       
                }
                else {
                    alert("没有获取相关数据!");
                    location.href = "";
                }
            })
        } else {
            //中国人
            AjaxSubmit('@Url.Action("ChinaJDCX", "YWCX")', { rylb: rylb, sfzh: sfzh, xm: xm }, null, function (data) {
                
                if (data.Result && data.Data != null) {

                    RestoreState();
                    location.href = "@Url.Action("WJSLBHCXJG", "YWCX")?rylb=" + rylb + "&sfzh=" + sfzh + "&xm=" + xm + "&type=0";
                    
                }
                else {
                    $("#lrv").html("没有获取相关数据！");
                    location.href = "";
                }
            })

        }      
    }
    // 记录恢复初始状态------返回时会恢复到初始的状态
    function RestoreState() {
        document.getElementById("select_zjlx")[1].selected = false;
        document.getElementById("select_zjlx")[2].selected = false;
        document.getElementById("select_zjlx")[3].selected = false;
        document.getElementById("select_zjlx")[4].selected = false;
        document.getElementById("select_zjlx")[0].selected = true;
        document.getElementById("sfzh").value = "";
        document.getElementById("xm").value = "";
    }