How can I access an JavaScript variable from within an JSP page ?
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4 Answers
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
});
5 Comments
Rachel
Can you provide an example of how can I access and client side variable's value on the server side ?
Dormilich
@Rachel: you would need either JavaScript make a request to the server (AJAX) or populate a form with the values and submit that.
T.J. Crowder
@Rachel: I added some examples
Rachel
@T.J.Crowder: Thank you for the example, now am able to understand this concept more clearly.
You can't access it directly. That's because this is how a page is rendered:
1. On the server, the JSP code runs and generates HTML/JavaScript.
2. The HTML/JavaScript is sent to the client's browser.
3. The browser then renders the HTML and runs the JavaScript.
As you can see, the JavaScript is run way after the JSP runs, so they can't directly access each other's variables.
What you could do is output JavaScript code which initializes a variable based on a value in the JSP code. For example, if you generate code like this (excuse my syntax, I don't know JSP):
<script>
var JSPValue = /*jsp code that prints the value of a variable*/;
//rest of JavaScript code...
</script>
Then the JavaScript can accss JSPValue, just because it will have been put there by the server. For example, when sent to the browser, it might look like:
<script>
var JSPValue = 42;
//rest of JavaScript code...
</script>
1 Comment
You suggestion of creating a global JavaScript variable does answer the question, but is not a recommended best practice. Dynamic creation of arbitrary global variables from JSP tends to lead developers who do not write for JavaScript primarily into a false sense of functionality that is prone to namespace collisions and unexpected code failure.
Not possible. You can access a JSP variable in javascript but the javascript variable can not be accessed in JSP.
answered May 22, 2010 at 18:14
Ravindra Gullapalli
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2 Comments
T.J. Crowder
You can't "access a JSP variable in [client-side] javascript". You can send the variable's value to the client by outputting it within the Javascript code in a server-generated
script block, which isn't the same thing.Rachel
Can you explain if it is possible to do it other way round ?
As the javascript is running on the client side and the JSp is running at the server side,it is not possible to access the javascript variable in jsp code,but u can acess that javascript variable in the server side by passing that variable along with the request as request parameters,As the request parameters are there in the request object which is available to jsp code ,u can access them.
