在上传到s3之前如何添加内容类型？

Question

我正在将文件发送到s3存储桶，然后再发送需要验证的文件是否为pdf，如果pdf需要将内容类型设置为application / pdf有人可以建议我是javascript新手吗

    add: function(e, data) {
            $('#upload-container').append('<div>* ' + data.files[0].name + '</div>');
            $('#upload-files').on('click', function(e){
                e.preventDefault();
                fileExtension = data.files[0].name.substr((data.files[0].name.lastIndexOf('.') + 1));
                console.log (fileExtension);
                if (fileExtension == "pdf"){
                  data.submit();
                  console.log(data.files[0]);
                }
                else{
                    alert("Please Upload Pdf file")
                }

            })
        },
        submit: function(e, data) {
            var fileName = data.files[0].name;
            content = data.files[0].type;
            console.log(content);
            if ($.inArray(fileName, fileNames) === -1){ fileNames.push(fileName); }
            else { return false; }
        },

这是我正在发送的ajax请求

  done: function (e, data) {
            var params = {
                file_name: data.files[0].name,
                debt_id: $('#debt-id')[0].value,
                category: $("select[name='document_category']")[0].value
            }

            $.ajax({
                type: 'POST',
                url: '/documents/create',
                data: params,
                error: function(response){
                    console.log('Something went weird, document not created.')
                    console.log(response)
                },
                success: function(response){
                    $('#upload-container').html('');
                    $('#progress .bar').css( 'width', '0%');

                    response = JSON.parse(response);

                    $('#debts_documents_list').prepend(
                            '<span class="date">' + response.document_date + '</span>' +
                            '<span class="title">' + response.document_title + '</span>' +
                            '<span class="type">' + response.document_category + '</span>' +
                            '<span class="download"><a href=' + response.document_url + ' target="_blank" class="btn_small">Download</a></span>'
                    );

                    /*
                     * closing the modal
                     */
                    $( ".pf4_modal" ).removeClass('active');
                    $( ".pf4_modal_bg" ).removeClass('active');
                    $( "body" ).removeClass('pf4_modal_body');
                    $(".modal_content_action .pf4_modal_upload_close_js").trigger('click');

                    //console.log('Document created on DB')
                    //console.log(response)

                }
            });
        },

快速回复应该会很有帮助