<input class="baixin-quan-info-box-time" type="text" onfocus="(this.type='date')" placeholder='起始时间' v-model="tnianxian1">

<input :class="'l-d-box-alone-ipt'+(yy_time?' full':'')" v-model="yy_time" onfocus="(this.type='date')" placeholder="select a date" type="date">

css:

input[type="date"].full:before {

            color: black;

            content: ""!important;

        }

        input[type="date"] {

            direction: ltr;

        }

input[type="date"]:before {

            color: #A9A9A9;

            content: attr(placeholder);

        }

js:

$("input[type='date']").on("input", function() {

                        console.log($(this).val().length)

                        if ($(this).val().length > 0) {

                            $(this).addClass("full");

                        } else {

                            $(this).removeClass("full");

                        }

                    });