how to pass the strMessage (from codebehind to the script) to get the alert message

Question

how to pass the strMessage (from codebehind to the script) to get the alert message

i.e if my strmessage from code behind is hi,

then i need

You Have Used already the message : hi

My code...

<script type="text/javascript">
     var strFileName;

    function alertShowMessage() {
    alert("You Have Used already the message :"+ <%=strFileName %>+ ");
    }
</script>


datatable dtChkFile =new datatable();
dtChkFile = objutility.GetData("ChkFileName_SMSSent", new object[] {"rahul"}).Tables[0];
         if (dtChkFile.Rows.Count > 0)
         {
             for (int i = 0; i < dtChkFile.Rows.Count; i++)
             {
                  strMessage= dtChkFile.Rows[i]["Message"].To);

             }
         }

Answer 1

In your code behind you could define a variable that will contain the message text:

public partial class _Default : System.Web.UI.Page
{
    public string SomeMessage = "Hello World";
}

And in the markup:

<script type="text/javascript">
function alertShowMessage() {
    alert('You Have Used already the message : <%= SomeMessage %>');
}
</script>

You should also be aware that when you use <%= SomeMessage %>, the message won't be encoded and if it contains some special characters such as ' it might break the javascript. This blog post contains a sample function that encodes strings used in javascript.

Answer 2

Depending on at what point you want the alert message to appear, consider using RegisterStartupScript / RegisterClientScriptBlock. Here's a sample (also using the AntiXSS library to javascript-encode the word to mitigate against quotes or any kind of XSS attack).

using Microsoft.Security.Application;

namespace RegisterClientScriptBlock
{
    public partial class _Default : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            String alertScript;
            String inputWord;
            String encodedWord;

            encodedWord = AntiXss.JavaScriptEncode(inputWord);

            alertScript = "function alertShowMessage() {";

            if (checkIfWordHasBeenUsed(inputWord) == true)
            {
                alertScript = alertScript + "alert('You have already used the message:" + encodedWord + "');}";
            }
            else
            {
                alertScript = alertScript + "alert('You have not used the message:" + encodedWord + "');}";
            }

            Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "alertShowMessage", alertScript, true);
        }
    }
}