利用js获取下拉框中所选的值

/// <summary>
/// 平台角色
/// </summary>
public enum AdministratorRole
{
 [Display(Name = "平台管理员")]
 PlatformAdministrator = 1,
 [Display(Name = "加盟商")]
 JoiningTrader = 10
}

<div class="form-group">
  @Html.LabelFor(x => x.AdministratorRole, new { @class = "col-sm-2 control-label" })
  <div class="col-sm-8">
   @Html.EnumDropDownListFor(x => x.AdministratorRole, new { @class = "form-control", onChange = "showSchool(this.value)", placeholder = Html.DisplayNameFor(x => x.AdministratorRole) })
  </div>
  <div class="col-sm-2">
   <div class="help-block">@Html.ValidationMessageFor(x => x.AdministratorRole)</div>
  </div>
 </div>
 <div class="form-group" style="display:none" id="schoolSelect">
  @Html.LabelFor(x => x.SchoolId, new { @class = "col-sm-2 control-label" })
  <div class="col-sm-8">
   @Html.DropDownListFor(x => x.SchoolId, Model.Schools, new { @class = "form-control", placeholder = Html.DisplayNameFor(x => x.SchoolId) })
  </div>
  <div class="col-sm-2">
   <div class="help-block">@Html.ValidationMessageFor(x => x.SchoolId)</div>
  </div>
 </div>

 <script type="text/javascript"> 
 function showSchool(v){  
  if (10 == v) {
   document.getElementById("schoolSelect").style = "display:inline";
  } else {
   document.getElementById("schoolSelect").style = "display:none";
  }
 }
</script>