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Atom.js is a small, easy to use JavaScript class that provides asynchronous control flow, event/property listeners, barriers, and more.


  • Small: 3.4kB minified, 1.5kB gzipped.
  • No dependencies: works in a browser, or in node.
  • Enables programming patterns that reduce the need for deeply nested callbacks and conditionals.


npm install atom-js

Unit Tests

To run from command line using node.js:

node test.js      // brief
node test.js -v   // verbose

To run in a browser, open test.html, or go here.


This is a.

    var a

a is an atom.

    var a = atom();


An atom has properties. The .get() and .set() methods may be employed to read and write values of any type.

    a.set('key', 'value');
    console.log('Value of key: ' + a.get('key'));
        pi: 3.141592653,
        r: 5,
        circumference: function () {
            return 2 * a.get('pi') * a.get('r');
    console.log('Circumference: ' + a.get('circumference')());

Parameters to the constructor will also be set as properties.

    a = atom('key', 'value');
    a = atom({ pi: 3.141592653, r: 5 });

Use .has() to query for existence of a property, and .keys() to get a list of all properties that have been set.

    if (a.has('game')) {
        console.log('What "a" brings to the table: ' + a.keys());

The .each() method lets you execute a function on a series of properties.

    a.set({ r: 0xBA, g: 0xDA, b: 0x55 });
    a.each(['r', 'g', 'b'], function (key, value) {
        console.log(key + '' + value);


Listeners may be attached to atoms in a variety of ways.

To be notified as soon as a property is set, use the .once() method. The callback will be called immediately if the property is already set.

    a.once('userInfo', function (userInfo) {
        alert('Welcome, ' + + '!');

Many atom methods can work with more than one property at a time.

    a.once(['userInfo', 'appInfo'], function (user, app) {
        alert('Welcome to ' + + '' + + '!');

When you just want to know about the next change, even if the property is already set, use .next().'click', function (click) {
        alert('Are you done clicking on ' + click.button + ' yet?');

To watch for any future changes to a property, use the .on() (alias .bind()) method.

    function myErrorHandler(error) {
        console.log('There was a grevious calamity of code in ' + a.get('module'));
    a.on('error', myErrorHandler);

Note that setting a property with a primitive (string/number/boolean) value will only trigger listeners if the value is different. On the other hand, setting an array or object value will always trigger listeners.

You can unregister any listener using .off() (alias .unbind()).;

If you only want to remove the listener associated with a particular key or keys, you can specify those too:['a', b'], myErrorHandler);

Needs and Providers

You can register a provider for a property.

    a.provide('privacyPolicy', function (done) {
        httpRequest(baseUrl + '/privacy.txt', function (content) {

Providers only get invoked if there is a need, and if the property is not already set. Use the .need() method to declare a need for a particular property. If a corresponding provider is registered, it will be invoked. Otherwise, .need() behaves just like .once().

    a.on('clickPrivacy', function () {
        a.need('privacyPolicy', function (text) {
            element.innerText = text;


Properties of two or more atoms can be entangled, using the .entangle() method. When an entangled property gets set on one atom, the value will instantly propagate to the other.

    var b = atom();
    a.entangle(b, 'email');
    a.set('email', '');
    console.log('Entangled email: ' + b.get('email'));

.entangle() also works when called with a list of properties.

    a.entangle(b, ['firstname', 'lastname']);

If called with a map of property names, then property 'X' on one atom can be entangled with property 'Y' on the other atom.

    a.entangle(b, { firstname: 'first', lastname: 'last' });
    a.set('firstname', 'Joe');
    console.log('Welcome, ' + b.get('first'));

Note that entangled properties are not actually synchronized until the first change after entanglement.

Asynchronous Queueing

String together a series of asynchronous functions using the .chain() method.

        function (nextLink) {
            callAjaxMethod('callThisFirst', function (firstResult) {
        function (nextLink, firstResult) {
            callAjaxMethod('callThisSecond', function (secondResult) {

Method Chaining

Not to be confused with the .chain() method specifically, "method chaining" actually refers to the practice of stringing together multiple method calls in a single expression.

    a = atom('start', new Date())
        .once('loaded', function () {
            console.log('Finished loading.');
        .once('shutdown', function () {
            console.log('Shutting down.');
        .set('loaded', true);

The .chain(), .each(), .entangle(), .mixin(), .need(), .next(), .off(), .on(), .once(), .provide() and .set() methods are all chainable.


Release references to all data and callback functions with the .destroy() method.


Additional Resources