用Javascript为DropDownList添加一个Item至定义索引位置

用Javascript为DropDownList控件下拉式选择添加一个Item至定义索引位置。

准备数据，创建一个对象，将是存储DropDownList控件每个Item数据。

Imports Microsoft.VisualBasic
Namespace Insus.NET

    Public Class Catalog

        Private _ID As Integer
        Private _Name As String

        Public Property ID As Integer
            Get
                Return _ID
            End Get
            Set(value As Integer)
                _ID = value
            End Set
        End Property

        Public Property Name As String
            Get
                Return _Name
            End Get
            Set(value As String)
                _Name = value
            End Set
        End Property

    End Class
End Namespace

在.aspx放置一个DropDownList控件：

<asp:DropDownList ID="DropDownListCatalog" runat="server"></asp:DropDownList>

在.aspx.vb绑定数据：

Imports Insus.NET

Partial Class _Default
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
        If Not IsPostBack Then
            Data_Binding()
        End If
    End Sub

    Private Sub Data_Binding()
        Me.DropDownListCatalog.DataSource = GetData()
        Me.DropDownListCatalog.DataValueField = "ID"
        Me.DropDownListCatalog.DataTextField = "Name"
        Me.DropDownListCatalog.DataBind()
    End Sub


    Private Function GetData() As List(Of Catalog)
        Dim cls As New List(Of Catalog)

        Dim cl As Catalog = New Catalog()
        cl.ID = 1
        cl.Name = "新闻频道"
        cls.Add(cl)

        cl = New Catalog()
        cl.ID = 2
        cl.Name = "体育频道"
        cls.Add(cl)

        cl = New Catalog()
        cl.ID = 3
        cl.Name = "军事频道"
        cls.Add(cl)

        cl = New Catalog()
        cl.ID = 4
        cl.Name = "教育频道"
        cls.Add(cl)

        Return cls
    End Function


End Class

准备数据与环境后，写Javascript:

 window.onload = function () {
            var catalog = document.getElementById("<%=DropDownListCatalog.ClientID%>");
            var obj = document.createElement("option")
            obj.text = "请选择..."
            obj.value = 0
            catalog.options.insertBefore(obj, catalog.options[0]);
        }

 
DEMO: