element-ui文件上传 做类型大小的限制

<div class="filebox">
    <el-upload class="upload-demo" :action="url" :on-preview="handlePreview" :on-remove="handleRemove" 
　　　　　　multiple :limit="limitnum" :on-exceed="handleExceed" :file-list="fileList" :beforeUpload="beforeAvatarUpload">
    <el-button size="mini" type="primary">点击上传</el-button>
    <div slot="tip" class="el-upload__tip">只能上传jpg/png文件，且不超过500kb</div>
    </el-upload>
</div>

　　　　　　beforeAvatarUpload(file) {                 
                var testmsg=file.name.substring(file.name.lastIndexOf('.')+1)                
                const extension = testmsg === 'xls'
                const extension2 = testmsg === 'xlsx'
                const isLt2M = file.size / 1024 / 1024 < 10
                if(!extension && !extension2) {
                    this.$message({
                        message: '上传文件只能是 xls、xlsx格式!',
                        type: 'warning'
                    });
                }
                if(!isLt2M) {
                    this.$message({
                        message: '上传文件大小不能超过 10MB!',
                        type: 'warning'
                    });
                }
                return extension || extension2 && isLt2M
            }