element上传图片限制方法

beforeCoverUpload: (file) => {
      const isLtM = file.size / 1024 / 1024 < 2;
      // 如果图片的大小超过 2MB 的话，直接 return false
      if (!isLtM) {
        Toast.warning('上传图片大小不能超过 2MB!')
        return false
      }

      return new Promise(function (resolve, reject) {
        let reader = new FileReader();
        reader.onload = function (event) {
          let image = new Image();
          image.onload = function () {
            let width = this.width;
            let height = this.height;

            console.log(width,height)
            if (width !== 1080 || height !== 1920) {
              Toast.warning('背景图片像素必须为1080*1920')
              reject();
            }
            resolve();
          };
          image.src = event.target.result;
        }
        reader.readAsDataURL(file);
      });
    },