【Element 】upload 限制上传图片尺寸、大小、比例

<el-upload
           class="upload-demo"
           :action="uploadLi"
            :before-upload="beforeUpload"
            :on-success="handleSuccess"
            :headers="{'X-User-Token': authorization}"
             name="file"
             accept="image/png,image/jpg,image/jpeg,image/gif"
             :multiple=false
             :show-file-list=false
              >
              <div class="avatar" v-if="createForm.advertPic">
                   <img :src="createForm.advertPic" class="avatar_img">
                    <span>修改图标</span>
              </div>
             <el-button size="small" type="primary" style="height:28px;" v-else>上传</el-button>
              <div slot="tip" class="el-upload__tip" style=&