How To Invoke Function At Server Side?

//First Of All Drag A Button From The Toolbox In The Window From & Then Put The Server Function In That Click Event….

protected void NewButton_Click(object sender, EventArgs e)
{
    ServerFunctionName();
}

//Now You Can Call That Function Using This Javascript Code.... Secondly, you can call the server function at JavaScript by using the following code,

document.getElementById("NewButton").click();