Use & Call RegisterStartUpScript, RegisterClientScript and Client-Side Script

RegisterStartupScript

Using RegisterStartupScript we can write a JavaScript function in code behind and call it from code-behind or from HTML. Look at the code below for reference.

Calling & Writing JavaScript Function from Server Side Code Behind

private void Page_Load(object sender, System.EventArgs e)
{
    string jScriptValidator;
    jScriptValidator="<script> function ReqFieldValidator()" + 
                " { if (document.forms[0].txtField.value == '') \n"; 
    jScriptValidator+="{ alert('TextBox cannot be empty') \n ";
    jScriptValidator+="return false; \n";
    jScriptValidator+="} \n";
    jScriptValidator+=" return true \n";
    jScriptValidator+=" } </script>";
    Page.RegisterStartupScript("regJSval",jScriptValidator);
    btnSubmit.Attributes.Add("onclick","return ReqFieldValidator()");
}

Writing JavaScript Function in Server Side Code Behind and Calling from HTML

//Server side

private void Page_Load(object sender, System.EventArgs e)
{
    string jScript;
    jScript="<script>function JavScriptFn(){alert" + 
      " ('Client Function in javascript is call')}</script>";
}

//HTML side
< A onclick="JavScriptFn()" >
< asp:Label id="Label1" runat="server" Width="281px" 
   ForeColor="#8080FF">Click to call Javascript function.
</asp:Label> >/A >

Writing JavaScript in HTML and Calling it from Code-behind

<Head >
        <script>
        
        function ReqField1Validator()
        { 
         if (document.forms[0].txtField1.value == '') 
            {
                alert('TextBox cannot be empty') 
                return false
            } 
                return true 
        } 
                
        </script>
    </Head >

private void Page_Load(object sender, System.EventArgs e)
{
    btnOK.Attributes.Add("onclick","return ReqField1Validator()");
}

RegisterClientScriptBlock

Suppose we want JavaScript code to be executed but not a function. In that case, we make use of RegisterClientScriptBlock.RegisterClientScriptBlock which helps to make server side code as well as client side code inline to each other.

private void btnClientBlock_Click(object sender, System.EventArgs e)
{
    string jScript;
    jScript="<script>alert ('Javascript block of code executed')</script>";
    Page.RegisterClientScriptBlock("keyClientBlock",jScript);
    lblSequencial.Text="Remaining part of the code executed";
}

ASP.NET 2.0 RegisterClientScriptBlock/RegisterStartupScript

One can call JavaScript client side function directly from code behind using RegisterStartupScript. If one wants JavaScript to be embedded into codebehind, then make use of RegisterClientScriptBlock:

<script>
    function fnShowMessage()
    {
        alert(" Invoke Javascript function from Server Side Code Behind ");
    }
    </script>

protected void Button1_Click(object sender, EventArgs e)
    {
        ClientScript.RegisterStartupScript
  (GetType(),"Javascript", "javascript: fnShowMessage(); ",true);
    }
    protected void Button2_Click(object sender, EventArgs e)
    {
        ClientScript.RegisterClientScriptBlock(GetType(), "Javascript", 
  "<script>alert('Record Added Successfully')</script>");
    }
Hope you find the above article helpful. Any suggestions are most welcome.
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