Edit in JSFiddle

<form>
    <p><label>Your name</label><input type="text" name="name" /></p>
    <p><label>Email</label><input type="text" name="email" /></p>
    <p><input type="checkbox" name="newsletter" /><label>Newsletter</label></p>
    <p><input type="checkbox" name="updates" /><label>Updates</label></p>
</form>

<p><input id="convert" type="checkbox" /><label>Convert values</label></p>

<p>Form data:</p>
<p id="json"></p>

$('input').change(function() {
    var convert = $('#convert').is(':checked');
    $('#json').html($.toJSON($('form').formParams(convert)));
});

body {
    font-family: Verdana;
}

p {
    margin: 10px 0;
}

form {
    border: 1px solid #505050;
    padding: 5px;
}

#json {
    color: #505050;
}

form label {
    display: block;
    float: left;
    width: 100px;
}