Adding a Javascript function from code-behind in Page

HI,

Why must we add Javascript function from code behind only at the Page_load function

public partial class WebForm5 : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
//this works
TextBox1.Attributes.Add("onkeydown", "javascript:alert('keydown')");
//TextBox1.Attributes.Add("onchange", "javascript:alert('change')");
}
protected void TextBox1_TextChanged(object sender, EventArgs e)
{
//this does not
TextBox1.Attributes.Add("OnKeyDown", "alert('Hello')");
//TextBox1.Attributes.Add("onkeydown", "javascript:alert(this);");
}
}

The first example added to the Page_Load() works whereas the second one does not

Hi cally,

Please add AutoPostBack property true and try to put some data in textbox then this alert will pop up because its written on textchange event of textbox.

"TextBox1" runat="server" AutoPostBack="true"

OnTextChanged="TextBox1_TextChanged" >Hello

Hi. As per your latest comment, Hello alert will come only when you change any value in textbox because Hello alert is present in the Text change event. Thanks

Hi Jignesh, no it is still not working , am I missing something. Thank you for your assistance so far. I have attached my aspx page as well. I am just testing with something simpler before I move on to the bigger picture

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
namespace WebApplication1
{
public partial class WebForm5 : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
//TextBox1.Attributes.Add("onkeydown", "javascript:alert('keydown')");
//TextBox1.Attributes.Add("onchange", "javascript:alert('change')");
//TextBox1.Attributes.Add("onkeydown", "alert('Hello')");
}
protected void TextBox1_TextChanged(object sender, EventArgs e)
{
//TextBox1.Attributes.Add("OnKeyDown", "alert('Hello')");
//TextBox1.Attributes.Add("onkeydown", "javascript:alert('keydown')");
TextBox1.Attributes.Add("onkeydown", "alert('Hello')");
}
}

}

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm5.aspx.cs" Inherits="WebApplication1.WebForm5" %>
"http://www.w3.org/1999/xhtml">
"server">
"form1" runat="server">
"TextBox1" runat="server" OnTextChanged="TextBox1_TextChanged" >Hello

Please first remove both line and try below line, it should work I have tried its working

No, I just uncommented it for example purpose. I even changed the case to lowercase in the TextBox1_TextChanged event, it still does not work.

Hi Cally,

Javascript is Casesensitive please change event name like below

TextBox1.Attributes.Add("onkeydown", "alert('Hello')");

Hey Hi. We can add JavaScript function from client side also and it is not required to add from code behind. The second onkeydown event don't fire because you already added onkeydown event in the pageload itself. Thanks.

7 Replies

Know the answer? Post it — somebody with the same question will find it here.

Jignesh Kumar7y ago
Hi cally,

Please add AutoPostBack property true and try to put some data in textbox then this alert will pop up because its written on textchange event of textbox.

"TextBox1" runat="server" AutoPostBack="true"
OnTextChanged="TextBox1_TextChanged" >Hello
Salman Beg7y ago
Hi. As per your latest comment, Hello alert will come only when you change any value in textbox because Hello alert is present in the Text change event. Thanks
Cally K7y ago
Hi Jignesh, no it is still not working , am I missing something. Thank you for your assistance so far. I have attached my aspx page as well. I am just testing with something simpler before I move on to the bigger picture
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace WebApplication1
{
    public partial class WebForm5 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            //TextBox1.Attributes.Add("onkeydown", "javascript:alert('keydown')");
            //TextBox1.Attributes.Add("onchange", "javascript:alert('change')");
            //TextBox1.Attributes.Add("onkeydown", "alert('Hello')");
        }

        protected void TextBox1_TextChanged(object sender, EventArgs e)
        {
            //TextBox1.Attributes.Add("OnKeyDown", "alert('Hello')");
            //TextBox1.Attributes.Add("onkeydown", "javascript:alert('keydown')");
            TextBox1.Attributes.Add("onkeydown", "alert('Hello')");
        }
    }
}

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm5.aspx.cs" Inherits="WebApplication1.WebForm5" %>



"http://www.w3.org/1999/xhtml">
"server">



    "form1" runat="server">


            "TextBox1" runat="server" OnTextChanged="TextBox1_TextChanged" >Hello

Adding a Javascript function from code-behind in Page_Load()