c# - Use of RegisterClientScriptBlockRegisterStartupScript in asp.net 3.5 - Stack Overflow

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I'm not able to understand what is the use of it.RegisterClientScriptBlock/RegisterStartupScript.

When we can directly write the JavaScript code in.js file then call it on the button

ex: 2

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

btnPostback.Attributes.Add("onclick","return ReqField1Validator()");

What will be the use of RegisterClientScriptBlock/RegisterStartupScript?

protected void btnPostback_Click(object sender, EventArgs e)  {
    System.Text.StringBuilder sb = new System.Text.StringBuilder();
    sb.Append(@"<script language='javascript'>");
    sb.Append(@"var lbl = document.getElementById('lblDisplayDate');");
    sb.Append(@"lbl.style.color='red';");
    sb.Append(@"</script>");

    if (!ClientScript.IsStartupScriptRegistered("JSScript")){
        ClientScript.RegisterStartupScript(this.GetType(), "JSScript", sb.ToString());
    }
}

Read few articles but they were not clear.

Any thoughts on this would be great.

I'm not able to understand what is the use of it.RegisterClientScriptBlock/RegisterStartupScript.

When we can directly write the JavaScript code in.js file then call it on the button

ex: 2

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

btnPostback.Attributes.Add("onclick","return ReqField1Validator()");

What will be the use of RegisterClientScriptBlock/RegisterStartupScript?

protected void btnPostback_Click(object sender, EventArgs e)  {
    System.Text.StringBuilder sb = new System.Text.StringBuilder();
    sb.Append(@"<script language='javascript'>");
    sb.Append(@"var lbl = document.getElementById('lblDisplayDate');");
    sb.Append(@"lbl.style.color='red';");
    sb.Append(@"</script>");

    if (!ClientScript.IsStartupScriptRegistered("JSScript")){
        ClientScript.RegisterStartupScript(this.GetType(), "JSScript", sb.ToString());
    }
}

Read few articles but they were not clear.

Any thoughts on this would be great.

• c#
• javascript
• asp

Share Follow edited Apr 7, 2020 at 12:56 Renan Araújo 3,6411111 gold badges4141 silver badges5252 bronze badges asked Aug 5, 2011 at 4:29 KumeeKumee 21111 gold badge44 silver badges1212 bronze badges

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2 Answers 2

Sorted by: Reset to default 4

RegisterStartupScript is used to register and execute javascript functions once the page finished loading, this javascript code executes before the onLoad event of page is raised. You can use it for multiple reasons, for example, you want to execute any particular javascript function depending on some variable value in your code behind.

On the other hand, RegisterClientScriptBlock is used to add a script block on the top of your page, similarly it provides you a way to work with both client side code and server code in your code behind.

In time, you might e across situations in which you will need to call a function in JavaScript depending on some variants in your code behind.

A very mon example would be to handle exception messages and then display them in a fancy way using JavaScript.

You might want to catch an exception like this:

public void TrySomethingAwesome(){
    try
    {
        //try to do something awesome
    }
    catch (Exception ex)
    {   
        ScriptManager.RegisterStartupScript(Page, typeof(Page), "showError",
            string.Format("ShowError({0});", "Oops! Something went wrong :("), true);
    }
}

And that way your JavaScript can take over and display the message in a fancy way :D

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