引入佈局檔案

<link href="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.3/css/select2.min.css" rel="stylesheet" />
<script src="https://unpkg.com/vue/dist/vue.js"></script>
<script src="https://cdn.bootcss.com/jquery/2.2.4/jquery.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.3/js/select2.min.js"></script>

/**
 * select2封裝
 */
Vue.directive('select2', {
    inserted: function (el, binding, vnode) {
        let options = binding.value || {};

        $(el).select2(options).on("select2:select", (e) => {
            // v-model looks for
            // - an event named "change"
            // - a value with property path "$event.target.value"
            el.dispatchEvent(new Event('change', {target: e.target})); //說好的雙向繫結，竟然不安套路

        });
    },
    update: function (el, binding, vnode) {
        for (var i = 0; i < vnode.data.directives.length; i++) {
            if (vnode.data.directives[i].name == "model") {
                $(el).val(vnode.data.directives[i].value);

            }
        }
        $(el).trigger("change");

    }
});

/*使用案例*/
/*
<select v-select2="" v-model="sale.carNum" required="required" class="form-control select">
    <option value=""></option>
    <option v-for="item in options.carId" :value="item.value">{{item.text}}</option>
</select>
*/