参考文档：element-resize-detector的github链接

1.安装element-resize-detector

npm install element-resize-detector

2.引入到script中

<script>
import elementResizeDetectorMaker from "element-resize-detector";
</script>

3.在mounted中使用

  mounted() {
    this.watchSize();
  },
  methods: {
      watchSize() {
      const _this = this;
      var erd = elementResizeDetectorMaker();
      erd.listenTo(this.$refs.fan, (element) => { // 这里的this.$refs.fan指定要监听的元素对象，对应的是<div ref="fan"></div>
        var width = element.offsetWidth;
        var height = element.offsetHeight;
        _this.$nextTick(() => { // 这里填写监听改变后的操作
          //const element_style = _this.$refs.gif1.style;
          //console.log("Size: " + width + "x" + height);
          //if (width > height) {
          //  element_style.height = "100%";
          //  element_style.width = "auto";
          //} else {
          //  element_style.height = "auto";
          //  element_style.width = "100%";
          //}
        });
      });
    },
  }