Checkbox Validation For Terms And Service

I'm working on a Ruby on Rails web app and I'm trying to add a quick and dirty client-side Javascript validation, to ensure that users click a checkbox agreeing to our Ts and Cs, before clicking the "Register" button submits their info.

I'll post the generated HTML, rather than the Rails stuff.

This is the button that shouldn't submit the form until the checkbox has been clicked:

<input name="commit" onClick="return check_agreed()" type="submit" value="Complete Registration" /> or <a href="/">Cancel</a>

First off, to confirm that the onClick actually checks check_agreed(), I kept check_agreed() simple, just popping up an alert then returning false.

<script language="JavaScript">
function check_agreed()
{
alert("check_agreed checked");
return false;
}
</script>

This seems to work fine - the alert pops up and nothing is submitted. I have a checkbox:

<input type="checkbox" name="terms_agreed">

I'd like this to be checked before the form can be submitted, so I've altered check_agreed() and added some debugging alerts.

function check_agreed()
{
alert("in check_agreed");

if(terms_agreed == checked)
{
alert("checked");
return true;
}
alert("Please agree to the Terms and Conditions");
return false;
}

So now the first alert, "in check_agreed" pops up, but then the form is submitted, with neither "checked" nor "Please agree..." popping up. This happens regardless of whether the checkbox has been clicked.


I'm sure I'm doing something wrong - it seems to be to do with referring to the checkbox. Should I be giving the checkbox's complete path, rather than referring to it by its name? I've tried to work out the correct path according to the DOM, but it still does the same thing.