1.window.open

	<!-- html -->
         <div class="form-item" style="align-items: flex-start;">
                    <div style="text-align: center;">
                        <el-upload
                                id="fileUrl"
                                ref="fileUrl"
                                :action="baseUrl+'upload/upFile'"
                                :headers="getLoginHeaders()"
                                :limit="1"
                                :on-success="uploadSuccess"
                                :before-remove="beforeRemove"
                                :accept="accept"
                                :file-list="fileList"
                        >
                        </el-upload>
                    </div>
                    <div style="text-align: center; position: absolute">
                        <el-button
                                   type="primary"
                                   size="mini"
                                   icon="el-icon-document"
                                   @click="download(fileList)">预览附件</el-button>
                    </div>

                </div>

  <!--  预览附件 js -->
        download :function(url){
            window.open(url[0].url);
 },

2.创建一个a标签

<!--  on-preview -->
<el-col :span="12">
                    <div class="form-item" style="align-items: flex-start;">
                        <div style="margin-top: 3px;">上传附件</div>
                        <el-upload
                                id="fileUrlAudit"
                                ref="fileUrlAudit"
                                :action="baseUrl+'upload/upFile'"
                                :headers="getLoginHeaders()"
                                :limit="1"
                                :on-success="uploadSuccess"
                                :before-remove="beforeRemove"
                                :accept="accept"
                                :file-list="fileList"
                                :on-preview = "openFile"
                        >
                            <el-button size="small" type="primary">点击上传</el-button>
                        </el-upload>
                    </div>
                </el-col>

<!-- js 预览附件 -->
        openFile: function (e) { // 点击上传的文件列表的文件的操作
            // console.log(e, "点击上传的文件列表的文件的操作");
            var a = document.createElement("a");
            // console.log(a, "创建a");
            var event = new MouseEvent("click");
            a.target = "_blank";
            a.download = e.name;
            a.href = JSON.parse(e.url)[0];//路径前拼上前缀，完整路径
            a.dispatchEvent(event);
        },