No, you can't. JavaScript is executed on the client side (browser), while the session data is stored on the server.
However, you can expose session variables for JavaScript in several ways:
In JSP you'd have something like:
<input type="hidden" name="pONumb" value="${sessionScope.pONumb} />
or:
<div id="product" data-prodnumber="${sessionScope.pONumb}" />
Then in JS:
// you can find a more efficient way to select the input you want
var inputs = document.getElementsByTagName("input"), len = inputs.length, i, pONumb;
for (i = 0; i < len; i++) {
if (inputs[i].name == "pONumb") {
pONumb = inputs[i].value;
break;
}
}
or:
var product = document.getElementById("product"), pONumb;
pONumb = product.getAttribute("data-prodnumber");
The inline example is the most straightforward, but if you then want to store your JavaScript code as an external resource (the recommended way) it won't be feasible.
<script>
var pONumb = ${sessionScope.pONumb};
[...]
</script>