vue加载数据时显示 变量未定义

created() {
    this.getData(); 
  },
  methods: {
    getData() {
      this.$ajax.get('/api/commodityCategory/list')
        .then(function(response) {
          let list = response.data;
          this.tag1 = list;
          console.log(response.data.data);
        })
        .catch(function(response) {
          console.log(response);
        });
    },

报错2navSet.vue?6fae:145 TypeError: Cannot set property 'tag1' of undefined

这个tag1在data里有定义