• §1. Synopsis
• §2. Installation Instructions
• §3. Build & Test Instructions
• §4. Quick API Reference
• §5. Support
• §6. Change Log
• §7. Credits
• §8. License
• §9. Notes

Anyone who’s been working long enough with JavaScript’s Date object would probably agree that it’s badly designed and buggy. I’d rather not dive into the messy details, except where absolutely needed, in the §4. Quick API Reference section.

tau.js¹ is a JavaScript date library, that I’ve built so that I could scratch this itch.

It’s minimal: It solely supports UTC dates, for now, and the only formatting option is the ISO 8601 extended format. tau.js is not a wrapper around the native Date, and here’s the point where it diverges from other established solutions². This means that the date mutation functions, otherwise provided by Date, had to be re-written from scratch and thoroughly tested. It also means the library is notably slower than alternatives, for now.

Download dist/tau.min.js.
Or, with Bower: Fire up a terminal window, and type the following command:

bower install tau.js

Then:

<script src="path/to/tau.js"></script>

Fire up a terminal window, and type the following command:

npm install tau.js

Then:

var Tau = require("path/to/tau.js");

Fire up a terminal window, and type the following commands:

git clone https://github.com/CristianTincu/tau.js.git
cd tau.js
npm install
npm run-script grunt

First, build the library (see above).

Then, if you want to run the tests server-side, with Node.js, fire up a terminal window, and type the following command:

npm run-script test

If you want to run the tests client-side, open test/test-runner.html in whatever browser you want to test against.

tau.js exposes the Tau pseudo-class to the environment on “load”, if the environment is a browser, or on “require”, if the environment supports CommonJS modules (e.g. Node.js).

• Tau()

Unlike the native Date, tau.js provides only one humble constructor.
Calling the constructor simply creates instances referencing the Unix epoch (00:00:00 UTC on the 1^st of January, 1970).

• Tau#setUtcYear()
• Tau#setUtcMonth()
• Tau#setUtcDate()
• Tau#setUtcHours()
• Tau#setUtcMinutes()
• Tau#setUtcSeconds()
• Tau#setUtcMilliseconds()

These methods allow you to manipulate Tau instances, with respect to UTC.

Unlike native Date’s equivalent methods, they support “chaining”.
This apparently minor detail can compensate—to a certain degree—the constructor’s intentional lack of flexibility:

var tau = new Tau().setUtcYear(2013).setUtcMonth(4).setUtcDate(3);

There’s one extremely important point, concerning these methods, that you should be aware of.
Let’s consider the following example:

var date = new Date(2013, 0, 30);
date.setUTCMonth(1);

The native Date moves the date reference to the 2^nd of March, as there’s no such thing as the 30^th of April. In a more general context, such a decision might cause trouble, as a naïve API consumer might not be aware that a call to Date#setUTCMonth() could, in fact, modify the month day, also. JavaScript’s Date object doesn’t provide any help in treating such cases.

In contrast:

var tau = new Tau().setUtcYear(2013).setUtcMonth(0).setUtcDate(30);
tau.setUtcMonth(1);

tau.js moves the tau reference to the 30^th of April, although that would be an invalid date. But you can check that, via the Tau#isValid() method.

Note that tau.js does handle date overflow, though, when its outcome is 100% predicatable. That happens when change might propagate “upwards”: Tau#setUtcMonth() might impact years, Tau#setUtcDate() might impact months, years, Tau#setUtcHour() might impact month days, months, years, and so on.

• Tau#isValid()

This method allows you to check if a Tau instance is valid.
Tau#setUtcYear() and Tau#setUtcMonth() are the only two methods that may produce invalid dates.

• Tau#getUtcYear()
• Tau#getUtcMonth()
• Tau#getUtcDate()
• Tau#getUtcHours()
• Tau#getUtcMinutes()
• Tau#getUtcSeconds()
• Tau#getUtcMilliseconds()

This methods behave pretty much like you’d probably expect.

• Tau#getUtcIsoString()

You can use this method to obtain a serialization of a Tau instance in the ISO 8601 extended format, with respect to UTC.

• Tau.getMaxDate()

This is a helper function that allows you to find the last valid month day, given a day and a month.

• Tau.VERSION

This property can be queried to find out the current tau.js release.
tau.js is semantically versioned³. See §6. Change Log for a brief release history.

• Tau.noConflict()

If the environment is a browser, this method would—if called—throw tau.js into “no conflict” mode⁴, and restore Tau to its previous owner, if any.

I’ve tested tau.js on the following environments:

• Chrome “latest” (26.0.1410.63)

• Chrome 4

• Firefox “latest” (20.0.1)

• Firefox 3.6

• IE 10

• IE 8

• IE 7

• IE 6

• Safari “latest” (6.0.4) on OS X

• Safari “latest” (5.1.7) on Windows

• Mobile Safari on iOS 6

• Opera “latest” (12.15)

• Node.js “latest” (0.10.5)

• 0.1.0 (2013-05-14)

Initial development release of tau.js.

• Cristian Tincu (@CristianTincu on GitHub and Twitter)

I made tau.js as an exercise, and as an experiment. You’re free to use it in your own exercises, experiments, or projects, whether they’re “closed” or “open”, commercial or non-commercial, “good” or “evil”, subject to the terms of the MIT License⁶.

See Tau on Wikipedia.

See Moment.js and XDate.

See Semantic Versioning.

I’ve borrowed this trick—as well as others—from Underscore.js.

See Underscore.js’s noConflict().

“Latest” means the current stable version of the respective environment, at the time I’m writing this text.

See LICENSE.md.