atomo

Clojure's Atom implementation in JavaScript.

From the Clojure docs:

Atoms provide a way to manage shared, synchronous, independent state.

On top of the above, atoms provide also validation and observation capabilities.

Installation

$ npm install atomo

Usage

Atoms are references to values that may change over time. The most basic operation on an atom is querying its current value:

var a = require("atomo");
 
var anAtom = a.atom(42);
anAtom.deref() === 42
// true

An atom's value can be set to another value:

anAtom.reset("foo");
 
anAtom.deref() === "foo"
// true

Alternatively, an atom's value can be transitioned to another value providing a function:

function increment(x) { return x + 1; }
 
var anAtom = a.atom(41);
anAtom.swap(increment);
anAtom.deref() === 42
// true

Validation

Atoms support validation through a validation function, and they will throw an exception whenever we try to set the atom's value to an illegal value.

function is42(x) { return x === 42 };
 
var anAtom = a.atom(42, {validator: is42});
 
anAtom.reset(43); // Error!
anAtom.swap(increment); // Error!

Observation

Atoms support adding and removing watches for listening to value changes. Watches are called with three arguments: the atom, the old value and the new value.

var anAtom = a.atom(42);
 
var watcher = function(theAtom, oldValue, newValue){
    console.log("Atom changed from", oldValue, "to", newValue);
};
 
anAtom.addWatch(watcher);
 
anAtom.swap(increment);
// Atom changed from 42 to 43
 
anAtom.reset(42);
// Atom changed from 43 to 42
 
anAtom.removeWatch(watcher);
 
anAtom.swap(increment);
anAtom.reset(42);

License

BSD 2-clause license, Copyright 2014 - 2015 Alejandro Gómez.