如何使用javascript导出excel文件格式的表单表

<display:table name="analyticBeans" id="user" export="true" style="width:750px" sort="list" requestURI="/generatePerformanceReport.htm">
     <display:caption><b>Assessment Name : ${assessment.assessmentName}</b></display:caption>
     <display:column property="id" title="Sr No." headerClass="sortable" class="srNo" />
     <display:column property="firstName" title="Name" headerClass="sortable" class="pgmkey" />
     <display:column property="markObtain" title="Marks Obtained" headerClass="sortable" class="pgmkey" />
     <display:column property="assessmentTotalMarks" title="Total Marks" headerClass="sortable" class="pgmkey" />
     <display:column property="subject" title="Subject" headerClass="sortable" class="pgmkey" />
     <display:setProperty name="export.pdf" value="true" />
     <display:setProperty name="export.pdf.filename" value="PerformanceReport.pdf" />
</display:table>
<input type="button" id="btnExport" onclick= "generateexcel()">Click for Save</input><disp