Passing a servlet variable into javascript

Question

I'm looking to pass a servlet variable, myVar that is passed into a JSP page, and pass it to JavaScript. The JavaScript is an external javascript that is included into the JSP page.

I have a button that calls the JavaScript function, but I'm unable to pass any of the variables that are passed into the JSP page through the servlet. The button is not a part of a form.

I've tried in a function in JavaScript to call:

var x = '<%=myVar%>';

AND

var x = '${myVar}';

AND

var x = '<%= (String)request.getParameter("myVar") %>';

However, x is always a string of what I inputted.

I'm not using AJAX or JQuery. Any ideas?

Example Code is a simplified version: (so the button is actually a drop down that calls the js when I change the value, however, I want other variables that are not part of the drop down to be called in changeCLass)

Servlet side:

request.setAttribute("otherVars","tests");

JSP:

<script type="text/javascript" src="external.js"></script>

<select name="vars" id="myVars" onchange="changeClass(this)">
<option value='1' selected="selected">1</option>
</select>

external.js included in JSP:

function changeClass(newVarX) {

    var newVarId =newVarX.value;
    var tID = '${otherVars}';

    alert(newVarId + " " + tID);
}

Output: 1 $(otherVars}

but output should be: 1 tests

@user1798546 simple way of doing it is creating a hidden field that stores the value and getting it from there. Another way is to pass the variable into the js function as a parameter <button onclick='someFunction(<%= (String)request.getParameter("myVar") %>)'> Call function</button> — Lyuben Todorov
– Lyuben Todorov, Commented Nov 4, 2012 at 19:36
It would be better to explain how your application behaves atm (with code sample) to have a better understanding and provide a better solution — Luiggi Mendoza
– Luiggi Mendoza, Commented Nov 4, 2012 at 21:01
"The JavaScript is an external javascript that is included into the JSP page" - could you post the JSP showing how you include this file? — Martin Wilson
– Martin Wilson, Commented Nov 4, 2012 at 21:22
BTW ${otherVars} won't work on its own- you'll need to use c:out or a similar tag eg <c:out value="${otherVars}"/> — Martin Wilson
– Martin Wilson, Commented Nov 4, 2012 at 21:28

Jan · Accepted Answer · 2012-11-05 21:58:18Z

3

This does not work, because your JavaScript file is not processed by the server. Possible solutions are:

Declare the variable tID globally in the JSP file.

JSP:

<script type="text/javascript" src="external.js"></script>
<script type="text/javascript">
    var tID = '${otherVars}';
</script>

<select name="vars" id="myVars" onchange="changeClass(this)">
    <option value='1' selected="selected">1</option>
</select>

JavaScript (external.js):

function changeClass(newVarX) {
    var newVarId = newVarX.value;
    alert(newVarId + " " + tID);
}

Have the JavaScript file also be processed. You may use a JSP file for the JavaScript and apply the correct content type:

JSP:

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

<select name="vars" id="myVars" onchange="changeClass(this)">
    <option value='1' selected="selected">1</option>
</select>

JavaScript (external.jsp --> note, that it's a JSP file, too, but the content type is set to text/javascript):

<%@ page language="java" contentType="text/javascript; charset=UTF-8" pageEncoding="UTF-8"%>
function changeClass(newVarX) {
    var newVarId = newVarX.value;
    var tID = '${otherVars}';
    alert(newVarId + " " + tID);
}

edited Nov 5, 2012 at 21:58

answered Nov 4, 2012 at 21:35

Jan

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1 Comment

Jan Over a year ago

Just edited the answer. In the second solution the JavaScript file is a JSP file, but the content type is set to text/javascript. This will make the server process the file, so Java code can be used.

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