Question

How can I access an JavaScript variable from within an JSP page ?

Answer 1

My guess is that you’re probably running Javascript on the client (in the browser), and Java in your JSP pages on the server. You can’t access a client-side variable on the server. You can send a client-side variable’s value from the client to the server for server-side processing. You’d probably do that via an Ajax call, or just by submitting a form.

Edit For example, this Javascript code sends the value of the foo variable to the server side page ‘test.jsp’ using the field name “foofield” (slightly different name to be clear). This uses Prototype, but jQuery, Closure, and all the other libs can do much the same thing, just with slightly different syntax:

Server-side Java (in the JSP) — this is just like getting fields from a form that’s been submitted:

String foo;

foo = request.getParameter("foofield");

Client-side Javascript (using Prototype’s Ajax.Request):

// Our client-side `foo` variable
var foo = "Hi there";

// Send it to the server via Ajax (Prototype version)
new Ajax.Request('test.jsp', {
    parameters: {foofield: foo},
    onSuccess: handleSuccess,    // Function to call on success; not shown
    onFailure: handleFailure     // Function to call on failure; not shown
});

If you prefer jQuery for the client-side, here’s that Prototype code rewritten for jQuery’s ajax function:

// Our client-side `foo` variable
var foo = "Hi there";

// Send it to the server via Ajax (jQuery version)
$.ajax({
    url: 'test.jsp',
    data: {foofield: foo},
    success: handleSuccess,  // Function to call on success; not shown
    error: handleFailure     // Function to call on failure; not shown
});