Mirror fields
HTML
Type something:
<input id="a" type="text" class="mirror cba" formirror="abc" placeholder="one">
<input id="b" type="text" class="mirror abc" formirror="cba" placeholder="two">
<input id="c" type="text" class="mirror bad" formirror="dab" placeholder="one">
<input id="d" type="text" class="mirror dab" formirror="bad" placeholder="two">
JavaScript
$('.mirror').on('keyup', function() {
$('.'+$(this).attr('formirror')).val($(this).val());
});