How to change a hidden input value just before submitting using javascript?

Question

I am a very beginner in javascript and I would like to change a single input value when the user selects an option with a form, thhen submit it to the same page.

here is the Html code:

<form id="form" action="thispage.jsp" method="post">
<input id="action_type" type="hidden" name="action_type" value="firstAction" />
<table class="choose">
    <tr>
        <td>Choose your test</td>
        <td><select id="select_test" name="test_name">
            <option value="test0"></option>
            <option value="test1"></option>
        </select></td>
    </tr>
</table>

And the javascript function:

form = document.getElementById("form");
action = document.getElementById("action_type");
select = document.getElementById("select_test");
select.onchange = function() {
    action.setAttribute("value", "otherAction");
    form.submit();
}

And this returns an Exception, what is wrong with this code ?

As I said to Fabian, it was a NullPointerException from org.apache.jsp.someGeneratedClass._jspService — floribon
– floribon, Commented Aug 31, 2012 at 16:59

AndreCruz · Accepted Answer · 2012-08-31 10:24:44Z

1

It doesn't seem to be a problem with JavaScript, but with your JSP code. Try debugging the code and check where it's failing.

answered Aug 31, 2012 at 10:24

AndreCruz

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Fabian Blechschmidt · Accepted Answer · 2012-08-31 09:25:35Z

1

I think the form is not defined. try to add a var before the form.

answered Aug 31, 2012 at 9:25

Fabian Blechschmidt

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1 Comment

floribon Over a year ago

I'm sorry, the actual source of my errors was nos in this portion of code. It's sad that I only get a NullPointerException from org.apache.jsp.someGeneratedClass._jspService as It's difficult to debug. Thanks anyway.

Russell Gutierrez · Accepted Answer · 2012-08-31 10:34:43Z

0

I think nullPointer shows because there is no selected option. Since the code does not have any innerHTML on it, you cant choose anything.

answered Aug 31, 2012 at 10:34

Russell Gutierrez

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