<div class="form-group" id="member_group">
  <label class="col-lg-3 control-label required">选择用户
  <span class="required">*</span>
  </label>
  <div class="col-lg-4">
  <select class="form-control" name="user_id[]" id="member_select" multiple="multiple"></select>
  </div>
</div>

//选择用户
$("#member_select").select2({
  ajax: {
    //请求的URL
    url: "{{ route('member.index') }}",
    //返回的数据类型
    dataType: "json",
    //延迟时间，毫秒
    delay: 500,
    //是否缓存
    cache: true,
    //查询数据
    data: function (params) {
      //params.term就是你搜索输入的参数
      return {
        search: params.term,
        page: params.page || 1
      };
    },
    //请求结果回调函数，data就是后端返回的数据
    processResults: function (data, params) {
      var data = data.data;
      var results = [];
      //循环数据，将数据压入results中
      //注意数据必须要有二个属性，id和text，分别对应option的value和文本
      //网上有些说无法选中元素，请先检查这里，你是否设置了id，并且不为空
      $(data.data).each(function (i, obj) {
        results.push({
          id: obj.id,
          text: obj.name
        });
      });
      return {
        results: results,
        pagination: {
          more: (data.current_page * data.per_page) < data.total
        }
      };
    }
  },
  placeholder: '选择用户',
  //是否多选
  multiple: true,
  allowClear: true
});

{
  "status_code":200,
  "message":"查询成功",
  "data":{
    "current_page":1,
    "data":[
      {
        "id":2006,
        "name":"用户1"
      },
      {
        "id":2005,
        "name":"用户3"
      },
      {
        "id":2004,
        "name":"用户3"
      }
    ],
    "first_page_url":"http://test.me/member/index",
    "from":1,
    "last_page":1,
    "last_page_url":"http://test.me/member/index",
    "next_page_url":"http://test.me/member/index",
    "path":"http://test.me/member/index",
    "per_page":1,
    "prev_page_url":null,
    "to":null,
    "total":3
  }
}

$("#spread_select").val([1, 2]).trigger("change");

var selObj = [
  {"id": 1, "name": "小徐"},
  {"id": 2, "name": "小张"},
  {"id": 3, "name": "小明"},
];
(function initSel(selObj) {
  if (selObj) {
    for (var ix = 0; ix < selObj.length; ix++) {
      var item = selObj[ix];
      var option = new Option(item.name, item.id, true, true);
      $("#member_select").append(option);
    }
    $("#member_select").trigger('change');
  }
})(selObj);