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How can I call a javascript function from server side

I try to call a javascript function from an other c# function but I have an error in my console
Uncaught ReferenceError: updateState is not defined
.ascx file
<script>
function updateState(){
console.log("test")
}
</script>
<button runat="server" ID="Btn_Modify_state" onserverclick="Btn_Modify_state_Click">
<i class="fas fa-edit"></i>
</button>
.ascx.cs file
protected void Btn_Modify_state_Click(object sender, EventArgs e)
{
ScriptManager.RegisterClientScriptBlock(this, this.GetType(), "script", "updateState();", true);
}
I don't know how to resolve that issue someone have any idea ?

You may have forgotten to register the script. Try this different approach instead.
<script runat="server">
public void Page_Load(Object sender, EventArgs e)
{
// Define the name and type of the client script on the page.
String csName = "updateState";
Type csType = this.GetType();
// Get a ClientScriptManager reference from the Page class.
ClientScriptManager cs = Page.ClientScript;
// Check to see if the client script is already registered.
if (!cs.IsClientScriptBlockRegistered(csType, csName))
{
// If not, redefine your script
var csText = $"
<script type=\"text/javascript\">
function updateState(){
console.log("test")
}
</script>";
cs.RegisterClientScriptBlock(csType, csName, csText.ToString());
}
}
</script>
Source : https://learn.microsoft.com/en-us/dotnet/api/system.web.ui.clientscriptmanager.registerclientscriptblock?view=netframework-4.8

The solution was to do that :
.ascx.cs
protected void Btn_Modify_state_Click(object sender, EventArgs e)
{
Page.ClientScript.RegisterStartupScript(this.GetType(), "script", "<script type='text/javascript'>updateState();</script>");
}

Call Javascript function multiple times from code behind

I have the following button event handler in C#. I would like to call the same javascript function with different paramater.
protected void Button1_Click(object sender, EventArgs e)
{
for (int i = 0; i < 10; i++)
{
string script = String.Format("test({0},{1})", i.ToString(), i.ToString() + 1);
this.Page.ClientScript.RegisterStartupScript(this.GetType(),
"testFunction", script, true);
}
}

define your js method like:
<script type="text/javascript">
function UpdateTime(time) {
document.getElementById("<%=lblTime.ClientID %>").innerHTML = time;
}
and then in your code behind, use:
protected void UpdateTime(object sender, EventArgs e)
{
string time = DateTime.Now.ToString("hh:mm:ss tt");
string script = "window.onload = function() { UpdateTime('" + time + "'); };";
ClientScript.RegisterStartupScript(this.GetType(), "UpdateTime", script, true);
}
Source and demo here

Asp.net JavaScript OnClick not working

What I'm trying to do is, when I click on the button it should show an alert box.
Here is the code.
protected void btnAdd_Click(object sender, EventArgs e)
{
string script = "<script type=\"text/javascript\">alert('abc 1');
</script>";
ClientScript.RegisterClientScriptBlock(this.GetType(), "Alert 1",
script);
Response.Redirect("~/Index.aspx");
}
It is working perfectly but when I put this same code in another page it does not work.
what are the things I have to look into? any suggestion please?

move your js code to client side
<asp:Button ID="btnAdd" OnClientClick="alert('alert');" OnClick="btnAdd_Click" runat="server"/>
protected void btnAdd_Click(object sender, EventArgs e)
{
Response.Redirect("~/Index.aspx");
}

May be you can try this - syntax may be wrong -
protected void btnAdd_Click(object sender, EventArgs e)
{
Response.Redirect("~/Index.aspx?Issuccess=1");
}
index.aspx page -
protected void Page_Load()
{
if(Request.QueryString["Issuccess"] != null && Convert.ToInt32(Request.QueryString["Issuccess"]) == 1)
{
string script = "<script type=\"text/javascript\">alert('abc 1');
</script>";
ClientScript.RegisterClientScriptBlock(this.GetType(), "Alert 1",
script);
}
}

Pass the last Parameter either True or False in ClientScript.RegisterScript and better you pass the alert message in this way.
Like This
protected void btnAdd_Click(object sender, EventArgs e)
{
ClientScript.RegisterClientScriptBlock(this.GetType(), "Alert", "alert('abc 1');",true);
Response.Redirect("~/Index.aspx");
}

Javascript confirm dialog coming up twice; Jumping back after clicking Element

Beginner here, so please be gentle.
I'm trying to ask the User for confirmation. When he accepts, my javascript invokes a Button to run some code behind. The code behind will run a JavaScript function which alerts, just so I can see if it all works. What happens is, that after my first confirm() dialog, a second dialog appears. After confirming again, the code runs and my second JavaScript function confirms by alerting. But after I press okay on that, the whole thing jumps back to my first function and I get into a loop!
ASPX:
<script type = "text/javascript">
function ConfirmComputerOverwrite(ComputerName) {
if (confirm("Overwrite present computer " + ComputerName + " ?"))
{
}
else
{
}
document.getElementById("Test").click()
}
function allworkedout()
{
alert("asdf");
}
Code behind:
public string ComputerName = "";
protected void Page_Load(object sender, EventArgs e)
{
string ComputerName = "Computer1";
this.ComputerName = ComputerName;
StringBuilder sb = new StringBuilder();
sb.Append("ConfirmComputerOverwrite('" + ComputerName + "');");
ScriptManager.RegisterStartupScript(this, GetType(), "ConfirmComputerOverwrite", sb.ToString(), true);
}
protected void Test_Click(object sender, EventArgs e)
{
StringBuilder sb = new StringBuilder();
sb.Append("allworkedout();");
ScriptManager.RegisterStartupScript(this, GetType(), "allworkedoutID", sb.ToString(), true);
}
Thanks in advance !

Unless you are using ajax, the whole page is reloaded after click, so your javascript is executed again, prompting for confirmation, etc...

javascript alert not firing

I have a new page with the following:
The Response.Redirect works, but I don't get a popup before hand...
Any ideas???
protected void Page_Load(object sender, EventArgs e)
{
if (Request.QueryString["timeout"] != null && Request.QueryString["timeout"].ToString().Equals("yes"))
{
Response.Write("<script>alert('Your Session has Timedout due to Inactivity');</script>");
Response.Redirect("Default.aspx");
}
}

The Response.Redirect call never returns the code to the user. It immediately redirects the user to the next page. From the MSDN on Response.Redirect: "Any response body content such as displayed HTML text or Response.Write text in the page indicated by the original URL is ignored."

The Response.Redirect redirects the browser and your JavaScript does not get executed.
Try redirecting in JavaScript instead:
protected void Page_Load(object sender, EventArgs e)
{
if (Request.QueryString["timeout"] != null && Request.QueryString["timeout"].ToString().Equals("yes"))
{
Response.Write("<script>" +
"alert('Your Session has Timedout due to Inactivity');" +
"location.href='Default.aspx';" +
"</script>");
}
}