Platform Support

The following shows process module APIs available for each platform.

	Linux (Ubuntu)	Raspbian (Raspberry Pi)	NuttX (STM32F4-Discovery)	TizenRT (Artik053)
process.nextTick	O	O	O	O
process.exit	O	O	O	O
process.cwd	O	O	O	O
process.chdir	O	O	O	O

※ On NuttX, you should pass absolute path to process.chdir.

Process

The process object is a global that provides information about, and control over, the current IoT.js process. As a global, it is always available to IoT.js applications without using require().

process.arch

• {string}

The arch property returns the processor architecture identifier that the IoT.js process is currently running on. For instance 'arm', 'ia32', 'x64', or 'unknown'.

process.argv

• {Array}

The argv property returns an array containing the command line arguments passed when the IoT.js process was launched. The first element is the path to the IoT.js program. The second element is the path of the JavaScript file currently being executed. The remaining elements will be any additional arguments passed via command line.

Example

To print out all command line arguments the following example could be used:

process.argv.forEach(function(val, idx) {
  console.log('index: ' + idx + ' value: ' + val);
});

process.env

• {Object}

The env property returns an object containing a few environment variables. The following environment elements can be accessed:

• HOME
• IOTJS_PATH which is set to /mnt/sdcard on NuttX by default.
• env contains 'experimental' if the IoT.js was build with experimental support.

Example

console.log('HOME: ' + process.env.HOME);
// prints: HOME: /home/user

process.exitCode

• {integer} Default: 0

The exitCode property can be used to specify the exit code of the IoT.js process. This will be used when the process exits gracefully, or exited via process.exit() without specifying an exit code.

Specifying an exit code for the process.exit() call will override any previous setting of process.exitCode.

process.iotjs

• {Object}

The iotjs property holds IoT.js related information in an object. The following keys can be accessed via this property:

• board specifies the device type on which the IoT.js is running currently. For instance 'artik05x', 'artik10', 'rpi2','stm32f4dis', or 'unknown'.

Example

console.log(process.iotjs.board);
// on Raspberry 2 it prints: rpi2

process.platform

• {string}

The platform returns the identification of the operating system the IoT.js process is currently running on. For instance 'linux', 'darwin', 'nuttx', 'tizenrt', or 'unknown'.

process.chdir(path)

• path {string} The path to change working directory to.

The chdir method changes the current working directory of the IoT.js process or throws an exception if the operation fails (for instance the path specified does not exist).

Example

try {
  process.chdir('/invalid/path');
} catch(err) {
  console.log('invalid path');
}
// prints: invalid path

process.cwd()

• Returns: {string}

The cwd() call returns the current working directory of the IoT.js process.

Example

console.log('Current dir: ' + process.cwd());

process.exit([code])

• code {integer} The exit code. Default: 0

The exit() method instructs the IoT.js to terminate the process synchronously with an exit status of code. If code is not specified, exit uses the process.exitCode value which defaults to 0. IoT.js will not exit till all 'exit' event listeners are called.

The process.exit() method call will force the process to exit as quickly as possible, ignoring if there is any asynchronous operations still pending.

In most situations, it is not necessary to explcitly call process.exit(). The IoT.js will exit on its own if there is no additional work pending in the event loop. The process.exitCode property can be set to exit code when the process exits gracefully.

If it is necessary to terminate the IoT.js process due to an error condition, throwing an uncaught error and allowing the process to terminate accordingly is advised instead of calling process.exit().

Example

To exit with a failure code:

process.exit(1);

The shell that executed the IoT.js should see the returned exit code as 1.

To set the exit code on graceful exit:

doSomeWork()
process.exitCode = 1;

process.kill(pid[, signal])

• pid {number}

• signal {number

  string} The signal to send, either as a string or number. Default: ‘SIGTERM’.

The process.kill() method sends the signal to the process identified by pid.

Signal names are strings such as 'SIGINT' or 'SIGHUP'. See [Signal Events] and [kill(2)] for more information.

This method will throw an error if the target pid does not exist. As a special case, a signal of 0 can be used to test for the existence of a process. Windows platforms will throw an error if the pid is used to kill a process group.

Even though the name of this function is process.kill(), it is really just a signal sender, like the kill system call. The signal sent may do something other than kill the target process.

process.on('SIGHUP', () => {
  console.log('Got SIGHUP signal.');
});

setTimeout(() => {
  console.log('Exiting.');
  process.exit(0);
}, 100);

process.kill(process.pid, 'SIGHUP');

process.memoryUsage()

Returns: {Object}

• rss {integer} the amount of space occupied in the main memory device
• heapTotal {integer} heap total size
• heapUsed {integer} currently allocated bytes
• peakHeapTotal {integer} peak allocated bytes
• external {undefined} this field is not implement yet

The process.memoryUsage() method returns an object describing the memory usage of the shadow-node process measured in bytes.This feature is disabled by default, You can enable it by compilation option jerry-memstat

Example

process.memoryUsage()

process.nextTick(callback, […args])

• callback {Function}
• ...args {any} Additional arguments to pass when invoking the callback

The nextTick method adds the callback method to the “next tick queue”. Once the current turn of the event loop is completed, all callbacks currently in the next tick queue will be called.

This is not a simple alias to setTimeout call. It runs before any additional I/O events.

Example

console.log('step 1');
process.nextTick(function() {
  console.log('step 2');
});
console.log('step 3');
// prints:
// step 1
// step 3
// step 2

process.version

• {string}

The version property returns the version numbering of the currently running IoT.js process as a string.

Example

console.log(process.version);
// prints: (in case of version 1.0.0)
// 1.0.0

process.versions

• {Object}

The process.versions property returns an object listing the version strings of ShadowNode and its dependencies.

console.log(process.versions);

Will generate an object similar to:

{
  "node":"0.8.0",
  "http_parser":"2.5.0",
  "uv":"1.10.1",
  "mbedtls":"2.4.0"
}

Event: ‘exit’

• callback {Function}
  • code {integer} exitCode

The 'exit' event is emitted when the IoT.js process is about to exit. This can happen two ways:

• The process.exit() method was called explicitly;
• The IoT.js event loop does not have any additional work to perform.

There is no way to prevent the exiting, and once all 'exit' listeners have finished running the process will terminate.

The listener callback function is invoked with the exit code specified either by the process.exitCode property, or the exitCode argument passed to the process.exit() method.

Listener functions must only perform synchronous operations. The IoT.js process will exit immediately after calling the 'exit' event listeners causing any additional work still queued to be abandoned.

Example

process.on('exit', function(code) {
  console.log('exited with: ' + code);
});

Event: ‘uncaughtException’

• callback {Function}
  • err {Error} error object uncaught by catch handler

The 'uncaughtException' event is emitted when an uncaught JavaScript exception bubbles all the way back to the event loop. By default, IoT.js handles such exceptions by printing it to stderr and exiting. Adding a handler for the 'uncaughtException' event overrides the default behavior.

The listener function is called with the Error object passed as the only argument.

Warning: Using the 'uncaughtException' event correctly

This event is a crude mechanism for exception handling intended to be used only as a last resort. The event should not be used as an eqivalent to ‘On Error Resume Next’. Unhandled exceptions inherently mean that a program is in an unknown state. Thus attempting to resume the application code without properly recovering from the exception can cause unforeseen/unpredictable issues.

Only one exception thrown within the event handler will be caught and will immediately terminate the application.

The correct use of the event is to perform synchronous cleanup of allocated resources (e.g. file descriptors, handles, etc) before shutting down the process. It is not safe to resume normal operation after this event.

To restart a crashed application in a more reliable way, whether uncaughtException is emitted or not, an external monitoring application should be employed in a separate process to detect application failures and recover or restart as needed.

Example

process.on('uncaughtException', function(err) {
  console.log('Something went wrong: ' + err);
});

nonExistentFunctionCall();
console.log('This will not be printed.');

Event: ‘uncaughtException’

The 'unhandledRejection' event is emitted whenever a Promise is rejected and no error handler is attached to the promise within a turn of the event loop. When programming with Promises, exceptions are encapsulated as “rejected promises”. Rejections can be caught and handled using promise.catch() and are propagated through a Promise chain. The 'unhandledRejection' event is useful for detecting and keeping track of promises that were rejected whose rejections have not yet been handled.

The listener function is called with the following arguments:

reason {Error | any} The object with which the promise was rejected (typically an Error object). p the Promise that was rejected.

process.on('unhandledRejection', (reason, p) => {
  console.log('Unhandled Rejection at:', p, 'reason:', reason);
  // application specific logging, throwing an error, or other logic here
});

somePromise.then((res) => {
  return reportToUser(JSON.pasre(res)); // note the typo (`pasre`)
}); // no `.catch()` or `.then()`

The following will also trigger the 'unhandledRejection' event to be emitted:

function SomeResource() {
  // Initially set the loaded status to a rejected promise
  this.loaded = Promise.reject(new Error('Resource not yet loaded!'));
}

const resource = new SomeResource();
// no .catch or .then on resource.loaded for at least a turn

In this example case, it is possible to track the rejection as a developer error as would typically be the case for other 'unhandledRejection' events. To address such failures, a non-operational .catch(() => { }) handler may be attached to resource.loaded, which would prevent the 'unhandledRejection' event from being emitted.

Signal Events

Signal events will be emitted when the ShadowNode process receives a signal. Please refer to signal(7) for a listing of standard POSIX signal names such as 'SIGINT', 'SIGHUP', etc.

The signal handler will receive the signal’s name ('SIGINT', 'SIGTERM', etc.) as the first argument.

The name of each event will be the uppercase common name for the signal (e.g. 'SIGINT' for SIGINT signals).

// Using a single function to handle multiple signals
function handle(signal) {
  console.log(`Received ${signal}`);
}

process.on('SIGINT', handle);
process.on('SIGTERM', handle);

signum specifies the signal and can be any valid signal except SIGKILL and SIGSTOP.

At the sigaction(2), the sigaction doesn’t support SIGKILL and SIGSTOP, therefore they are not supported at ShadowNode.