This code is a NetSuite Wizard or NetSuite Assistant which has a File Upload functionality.

netsuite_file_upload_wizard_css.js

/**
 * Executes when the wizard page loads. Binds a function/callback on the Browse button.
 * @returns {Void}
 */

function onPageInit() {
  var fileUploadButton = jQuery('#browse');

  if (fileUploadButton.length == 0) return;

  nlapiRemoveSelectOption('custpage_file', null);
  nlapiInsertSelectOption('custpage_file', '', 'Please upload a File', true);

  /* Bind the click event on the Browse button. */
  fileUploadButton.on('click', function () {
    /* Determine the File Upload Suitelet URL. */
    var fileUploadSuiteletURL = nlapiResolveURL('SUITELET', 'customscript_file_upload_slet', 'customdeploy_file_upload_slet') + '&l=T';

    var width = 480;
    var height = 200;
    var left = (screen.width / 2) - (width / 2);
    var top = (screen.height / 2) - (height / 2);

    /* Open the File Upload suitelet on the center of the wizard screen. */
    window.open(fileUploadSuiteletURL, 'UploadFile', 'toolbar=no, location=no, directories=no, status=no, menubar=no, scrollbars=no, resizable=no, copyhistory=no, width=' + width + ', height=' + height + ', top=' + top + ', left=' + left);
  });
};

/**
 * This is the function that will be called by the Suitelet when it is submitted.
 * The suitelet will pass the ID of the file uploaded and it's file name.
 * @param {String} fileId - The id of the file uploaded
 * @param {String} fileName - The name of the file uploaded
 * @returns {Void}
 */

function setFile(fileId, fileName) {
  nlapiRemoveSelectOption('custpage_file', null);
  nlapiInsertSelectOption('custpage_file', '', 'Please upload a File', false);
  nlapiInsertSelectOption('custpage_file', fileId, fileName, true);

  nlapiSetFieldValue('custpage_file', fileId, true, false);
  nlapiSetFieldValue('custpage_file_name', fileName, true, false);
}