Send FormData object AND an additional parameter via ajax

Try:

var formData = new FormData();
formData.append('file', this.files[0]);
formData.append('CustomerId', 2);

/*
 note:: appending in form Data will give "csrf token mismatch error". 
 so better you make a input feild of type hidden with name = CustomerId 
 and value =  2 
*/ 

$.ajax({
   url: urlUploadProductsFile,
   type: 'POST',
   data: formData,
   cache: false,
   contentType: false,
   processData: false
}, 'json');

You need to either add it directly to formData (just as you did with 'file'), or alternatively use query (GET) parameters.