How to use scriptlet inside javascript

Question

Can someone test this example and share the results? http://timothypowell.net/blog/?p=23
When I do:

var myVar = '<% request.getContextPath(); %>';
alert(myVar);

I get : '<% request.getContextPath(); %>'.

Removing the enclosing single quotes from '<% request.getContextPath(); %>'; gives syntax error. How can I use the scrptlet or expresion inside a js function?

EDIT: this link has an explanation that helped me:
http://www.codingforums.com/showthread.php?t=172082

Answer 1

That line of code has to be placed in a HTML <script> tag in a .jsp file. This way the JspServlet will process the scriptlets (and other JSP/EL specific expressions).

<script>var myVar = '<%= request.getContextPath() %>';</script>

Note that <%= %> is the right syntax to print a variable, the <% %> doesn't do that.

Or if it is intended to be served in a standalone .js file, then you need to rename it to .jsp and add the following to top of the file (and change the <script src> URL accordingly):

<%@page contentType="text/javascript" %>
...
var myVar = '<%= request.getContextPath() %>';

This way the JspServlet will process it and the browser will be instructed to interpret the JSP response body as JavaScript instead of HTML.

---

Unrelated to the concrete problem, note that scriptlets are considered poor practice. Use EL.

var myVar = '${pageContext.request.contextPath}';

Answer 2

It sounds like you are placing the JSP code within a JavaScript page, or at least in a non-JSP page. Scriptlets can only be included in a JSP page (typically configured to be *.jsp).

The statement as presented, if processed by the JSP compiler, would result in myVar being equal to '' as the scriptlet format you are using <% ... %> executes Java code between the tags, but does not return a result.

So, to use this tag you would need to manually write a value to the request output stream. To get the desired functionality you need to do the following:

  make sure your code is in a JSP page
  use var myVar = '<%= request.getContextPath() %>'; (note the equals sign)

With all that said, scriptlets are viewed as bad practice in most cases. For most cases, your should be using JSTL expressions and custom tags.

Answer 3

You cannot run scriptlet inside javascript by giving it normal .js extension. However you can give your .js the file extension of .jsp and then and link directly to it as:

<script type="text/javascript" src="/script.jsp"></script>

and now you can use jsp within your javascript like:

var someMessage = "${someMessage}"
var anotherMessage = "${anotherMessage}"/>"

This action is completely valid because what determines whether a file is a javascript file or not is what MIME media type. You can set MIME from JSP using:

<%@ page contentType="text/javascript" %>