API Reference: IO.File

File is an interface for accessing the filesystem of the operating system. 'path' is a required property for the construction of the File object.

Permission Management for File Operations

File operations needs permissions for Android. But for some file operations you don't need any permission as described in Google Developers. When you are reading/writing Path.DataDirectory you don't need any permission, but while you are reading/writing any of path you need READ_EXTERNAL_STORAGE or WRITE_EXTERNAL_STORAGE permissions.

For more information about how to manage permission in Smartface Native Framework, please visit Application Permission Management

File operations on iOS

You don't need any permission management on iOS for file operations.

const Page = require("sf-core/ui/page");
const extend = require("js-base/core/extend");
const File = require('sf-core/io/file');
const Path = require('sf-core/io/path');
var Page1 = extend(Page)(
function(_super) {
var myImage = new File({
path: 'images://smartface.png'
// Checking image file if exists
if (myImage.exists) {
var destinationFile = new File({
path: Path.DataDirectory + '/myImage.png'
// If destination file exists and file sizes identical no need to copy
if(!(destinationFile.exists && myImage.size === destinationFile.size)){
module.exports = Page1;

Caching Data With File

File can be used like buffer in memory that holds uncompressed data blocks. A better way to retrieve relatively constant data is to use caching objects to cache the data as you retrieve it.

// Cache some large data
var largeDataToBeCached = {};
const filePath = Path.DataDirectory + '/file.json';
var content = readFile(filePath);
if (!content) {
// First time creation
createFile(filePath, JSON.stringify(largeDataToBeCached));
else {
// File has already been created
function createFile(path, content) {
var file = new File({ path });
var fileStream = file.openStream(FileStream.StreamType.WRITE, FileStream.ContentMode.TEXT);
function readFile(path) {
var file = new File({ path });
var content = null;
if (file.exists) {
var fileStream = file.openStream(FileStream.StreamType.READ, FileStream.ContentMode.TEXT);
content = fileStream.readToEnd();
return content;