Google App Script function to create a Google Spreadsheet in a particular Google Drive folder

createSpreadsheet_.js

/**
 * Function to create a Google Spreadsheet in a particular Google Drive folder
 * @param {Object} targetFolder - Google Drive folder object in which you want to place the spreadsheet
 * @param {string} ssName - name of spreadsheet 
 * @return {string} ssId - spreadsheet ID of created spreadsheet
 */
function createSpreadsheet_(targetFolder, ssName) {
  var ssId = SpreadsheetApp.create(ssName).getId();
  var temp = DriveApp.getFileById(ssId);
  targetFolder.addFile(temp);
  DriveApp.getRootFolder().removeFile(temp);
  return ssId;
}

A Google Docs version of this script will be:

/**
 * Function to create a Google Docs file in a particular Google Drive folder
 * @param {Object} targetFolder Google Drive folder object in which you want to place the document
 * @param {string} docName Name of document 
 * @return {string} Document ID of created spreadsheet
 */
function createDocument_(targetFolder, docName) {
  var docId = DocumentApp.create(docName).getId();
  var temp = DriveApp.getFileById(docId);
  targetFolder.addFile(temp);
  DriveApp.getRootFolder().removeFile(temp);
  return docId;
}