jQuery принять только файл Excel
<input type="file" ID="fileSelect" accept=".xlsx, .xls, .csv"/>
Comfortable Capybara
<input type="file" ID="fileSelect" accept=".xlsx, .xls, .csv"/><input type="file" id="img" name="img" accept=".csv, application/vnd.openxmlformats-officedocument.spreadsheetml.sheet, application/vnd.ms-excel"><input id="fileSelect" type="file" accept=".csv, application/vnd.openxmlformats-officedocument.spreadsheetml.sheet, application/vnd.ms-excel" />