Where to use ASP and where not to use ASP
A useful way to decide between Classic ASP and browser-side code is to ask where the information and authority live. ASP runs on the server during a request; JavaScript runs in the browser after the response reaches the user.
Use ASP for a server-side check
<%@ Language=VBScript %>
<%
Dim qty
qty = 3
If qty > 0 Then Response.Write "In stock"
%>The result comes from server-side VBScript. For real inventory or authorization, retrieve trusted data on the server before evaluating a condition.
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Displaying an alert or reacting instantly to a click
That is a browser-side task, so use JavaScript. ASP can decide what HTML or JavaScript to send, but it cannot react to a later browser event unless the browser makes another request (for example through a form submission or AJAX).
Authenticating a user
Authentication and authorization decisions belong on the server. The browser can collect a user ID and password, but the server must verify the credentials and decide whether the user may access protected data. Client-side code must never be treated as the security boundary.
Validating form data
Use client-side validation to improve usability, but always validate important data again on the server. A visitor can disable or bypass browser JavaScript and can send requests directly to the server. See the client-side validation tutorial and the server-side regular-expression examples.
This server/client distinction becomes especially important in the database, login, session, and form-processing tutorials later in this section.
Choose the right execution environment
A browser can display a message immediately, but it cannot replace server-side authorization or database validation. A client-side check is not a security boundary.
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Subhendu Mohapatra
Author & Instructor at plus2net
I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.
