找input 的　id=”test”
httpsss://js.do/powenko/01-find-input-id

<script src="//ajax.googleapis.com/ajax/libs/jquery/3.1.0/jquery.min.js"></script>

<input id="test1" list="values" placeholder="select">
<datalist id="values">
    <option value="orange">
    <option value="banana">
    <option value="lemon">
    <option value="apple">
</datalist>
<script>
    $('input #test1').on('click', function() {
        $(this).attr('placeholder',$(this).val());
        $(this).val('');
    });
    $('input #test1').on('mouseleave', function() {
        if ($(this).val() == '') {
            $(this).val($(this).attr('placeholder'));
        }
    });
</script>
<!-- edit your html here -->