Vue.directive('load-more', {
    bind(el, binding) {
        // 获取element-ui定义好的scroll盒子
        const SELECTWRAP_DOM = el.querySelector('.el-select-dropdown .el-select-dropdown__wrap');
        SELECTWRAP_DOM.addEventListener('scroll', function () {
            const CONDITION = this.scrollHeight - this.scrollTop <= this.clientHeight;
            if (CONDITION) {
                binding.value();
            }
        })
    }
});