判断上传文件是否是Excel文件

<script language="javascript">
function doCheck(varCurObj) {
var varCurValue = varCurObj.value;
var varSufType = varCurValue.substring(varCurValue.lastIndexOf(".") + 1, varCurValue.length);

if (varCurValue.length == 0) {
document.getElementById("btnTrue").style.display = "none";
document.getElementById("btnFalse").style.display = "block";
} else {
if (varSufType.toLowerCase() != "xls") {
document.getElementById("btnTrue").style.display = "none";
document.getElementById("btnFalse").style.display = "block";
} else {
document.getElementById("btnTrue").style.display = "block";
document.getElementById("btnFalse").style.display = "none";
}
}
}
</script>

<input type="file" id="fleItem" name="fleItem" onchange="doCheck(this);" contentEditable="false" style="width: 300px;">
<input type="button" id="btnTrue" value="True" style="display: none;">
<input type="button" id="btnFalse" value="False" style="display: none;">