Tempus Fugit

Tempus fugit is a Latin expression meaning "time flees", more commonly translated as "time flies". It is frequently used as an inscription on clocks.

This module contains high level api for scheduling jobs and also exposes utilities and classes to help build other more custom / complex scheduling code.

Install

	npm install tempus-fugit

Usage

Scheduling api

The scheduling api can be used to schedule single time or repeating jobs. Repeating jobs schedule is defined using the interval object (see below).

schedule a one time job in the future:

var schedule = require('tempus-fugit').schedule;

var futureDate = new Date(....);
function task() {}

var job = schedule(futureDate, task);

// can cancel
job.cancel();

job = schedule(1000, task); // schedule in 1 second from now

schedule a repeating / recurring job:

var schedule = require('tempus-fugit').schedule;

var interval = { hour: 1, minute: 5 }; // every hour and 5 minutes

// job.done() is not required when overlappingExecutions is true
function task(job) { 
	// this.done() also works
	// also job.callback() can be used to create a callback function instead, e.g fs.readFile('foo', job.callback())
	job.done(); 
}

var job = schedule(interval, task /*, {.. options ..} */);

// can cancel
job.cancel();

scheduling options:

unref: [boolean] (default false) setting this to true will issue automatic unref() on timers, which will allow the node process to exit when a task is run.

overlappingExecutions: [boolean] (default false) setting this to true will cause tasks to overlap if they dont finish before interval time elapses.

createOnly: [boolean] (default false) if set to true execute() will not be called, this means you will have to call job.execute() after shceduling.schedule(...)

the interval object:

var interval = {
	millisecond: 1,
	second: 2,
	minute: 3,
	hour: 4,
	day: 5,
	start: Date.now() + 10000 || new Date('some date in the future') //optional
}

The interval object supports all the time units displayed above, those can also be used in combination to create more complex intervals (e.g day + hour + second). When scheduling a task using an interval object, tempus-fugit will sync the execution cycle to the next round occurance of the interval.

For example, look at the following code:

schedule({ hour: 1 }, function task (job) { job.done() })

If initially run at 20:31, will execute task at 21:00, then 22:00, then 23:00 etc...

If we want to start the cycle right away we can use the optional start property:

schedule({ hour: 1, start: Date.now() }, function task (job) { job.done() })

If initially run at 20:31, will execute task at 20:31, then 21:31, 22:31 etc...

Creating new job "classes"

	var AbstractJob = require('tempus-fugit').AbstractJob;
	var $u = require('util');

	$u.inherits(MyJob, AbstractJob);
	function MyJob(task, options) {
		AbstractJob.call(this, task, options)
	}

	// must implement
	MyJob.prototype._executeImpl = function () {
		return setInterval(this._task, 500);
	};

	// must implement
	MyJob.prototype._cancelImpl = function(token) {
		return clearInterval(token);
	};

	// optionally implement, if so, do no pass task argument in constructor
	MyJob.prototype._task = function () {
		console.log('foo!');
	};

Interval util

tu.intervalObjectToMillis():

var tu = require('tempus-fugit').temporalUtil;

var interval = { millisecond: 500, second: 2 };

console.log(tu.intervalObjectToMillis(interval));

will print:

2500

tu.normalizeIntervalObject:

var tu = require('tempus-fugit').tu;

var interval = { millisecond: 1502, second: 2 };

console.log(tu.normalizeIntervalObject(interval));

will print:

{ millisecond: 502, second: 3 }

note: this will modify the original interval object

tu.intervalCountSinceEpoch:

var tu = require('tempus-fugit').tu;

var interval = { day: 1 };

var n = Date.UTC(2000, 0);

var millis = tu.intervalObjectToMillis(interval);

console.log(tu.intervalCountSinceEpoch(millis, n));

will print:

10957

which is 30 years * 365 day + 7(.5) days from leap years

note: the n argument is optional, if omitted the function will use Date.now() internally

tu.nextIntervalEvent:

var tu = require('tempus-fugit').tu;

var interval = { day: 1 };

var n = Date.UTC(2000, 0, 1, 0, 30); // Sat Jan 01 2000 00:30:00 GMT

var millis = tu.intervalObjectToMillis(interval);

var nextInterval = tu.nextIntervalEvent(millis, n);

console.log(new Date(nextInterval).toUTCString());

will print:

Sun, 02 Jan 2000 00:00:00 GMT

note: the n argument is optional, if omitted the function will use Date.now() internally

Date related util

tu.nextSecond(date);

tu.nextMinute(date);

tu.nextHour(date);

tu.nextDate(date);

tu.nextMonth(date);

tu.nextYear(date);

example

	var tf = require('tempus-fugit');

	var now = new Date(2013, 11, 25, 23, 23, 59, 123);
	var actual = tf.tu.nextSecond(now);  // tf.tu === tf.temporalUtil

	console.log('closest second:');
	console.log(now);
	console.log(actual);

will print:

Wed Dec 25 2013 23:23:59 GMT+0200 (Jerusalem Standard Time)

Wed Dec 25 2013 23:24:00 GMT+0200 (Jerusalem Standard Time)

A Pitfall

I should probably find a solution for this, but for now, if you run a SeriallyRepeatingJob like this one:

schedule({ /*some interval data*/ }, function (job) {})

Calling job.done() will created a timer. But in this case we don't, if there are no other pending tasks in the event loop the process will exit.

TODO

• support month and year intervals, calculated correctly
• throw exception from jobs if error event is not handled or ignore errors flag is not set
• add more events to job