W3C APIs
Tabris implements a subset of popular W3C standards. Besides providing web developers with familiar APIs, this also enables you to use libraries developed for a browser environment.
window object
In JavaScript there is always an object that represents the global scope. All global variables are members of this object. For compatibility this object is available as window, but global is the actual global object in Tabris.js. For example, the tabris object can be accessed either via tabris or global.tabris or window.tabris.
console object
As in the browser, messages can be logged to the developer console using the global console object:
console.log("A log message");
console.warn("A warning message");
console.error("An error Message");
console.trace();
Calling console.error will also cause a message to pop up (even if the developer console is closed), but it won’t interrupt script execution. See Console.
Timer
Tabris supports the timer methods setTimeout, setInterval, clearTimeout and clearInterval. See timer.
Fetch
Tabris supports the Fetch API to make HTTP request and to read resources that are part of the application.
When a relative URL is given, Tabris.js will interpret it as a path relative to the application’s main package.json. This allows you to read static resources, i.e. the files residing in your project folder and not excluded via .tabrisignore. You can also use URLs relative to the current module by using the __dirname variable, e.g. fetch(__dirname + "/foo.txt");.
To enable access to SSL protected resources that use self signed certificates add them to
app.trustedCertificates. Alternatively you can disable theUseStrictSSLpreference in the config.xml to accept all certificates. See Building a Tabris.js App.
XMLHttpRequest
Tabris also supports XMLHttpRequest, though fetch() is recommended for convenience.
WebSocket
WebSockets are an advanced technology that makes it possible to open an interactive communication session between the user’s client and a server. With this API, you can send messages to a server and receive event-driven responses without having to poll the server for a reply.
The Tabris.js implementation supports to send and receive text messages as well as binary data in the form of
TypedArrayandArrayBuffer, but notBlob.
Worker
Workers are a simple mechanism to run a script in a background thread. The worker thread can perform tasks without interfering with the user interface. In addition, they can perform I/O using XMLHttpRequest or the file system api. Once created, a worker can send messages to the JavaScript code that created it by posting messages to an event handler specified by that code (and vice versa).
The tabris support for workers allows to send data to a running worker via the worker.postMessage(data, transferList) method. The transferList is ignored. The types supported in the data field are:
nullundefinedstringnumberBooleanObjectArrayImageDataArrayBufferArrayBufferView/TypedArray
Only the following Tabris.js APIs can be used in a worker:
- localStorage
- App (Except:
restart(),close()andcloseKeyboard()) - Crypto
- Device
- file system
- XHR/fetch
- TextEncoder
- WebSocket
- Worker
Widget APIs are unavailable. Calling any unsupported APIs has no effect.
Persistent Storage
Tabris supports the global object localStorage, which allows storing key-value pairs in a persistent store. Both keys and values are stored as strings. See also localStorage.
Note that the “storage” event is not supported. For debugging purposes the contents of the localStorage can be inspected using console.dirxml()[./api/console.md#dirxml]. On iOS, there is an additional object secureStorage available in the global scope. This is a drop-in replacement for localStorage that keeps data in the encrypted iOS Keychain.
localStorageis only meant to store relatively short strings. To store larger amounts of data it is recommended to use the cordovaFileSystemplugin.
Canvas Context
The Canvas widget provides an HTML5 canvas compatible “2D Context” object. See Canvas.
Random Source (Crypto)
The global object crypto provides an implementation of the RandomSource interface. It can be used to generate cryptographically secure random numbers.
