Atom

Manage and observe state changes in JavaScript, based on Clojure(Script) atoms.

Usage

var atom = require('atom');

var gabriel = atom({likes: "ice cream"});

gabriel.addWatch("logger", function(state) {
  console.log(state);
});

gabriel.state // => {likes: "ice cream"}

gabriel.swap(function(state) {
  return {likes: "cookies"};
});

// {likes: "cookies"} will be logged in the console

gabriel.state // => {likes: "cookies"}

Rationale

I want a clear distinction between state and identity.

Creating an atom

atom(state)

Creates a new atom with initial state.

Getting the atom state

a.state

Returns the current state for the atom a.

Updates

a.reset(state)

Sets the state of atom a to state.

a.swap(f, ...args)

Sets the state of atom a to the result of applying the function f to the current state, a.state, and the provided args.

function setLike(state, food) {
  return Object.assign({}, state, {likes: food});
}

a.swap(setLike, "hamburguers");
a.state.likes // => "hamburguers"

a.mreset(meta, state)

Like reset but it will pass the metadata meta to the watches.

a.mswap(meta, f, ...args)

Like swap but it will pass the metadata meta to the watches.

Observation

a.addWatch(key, f)

Invoke the function f every time the state of the atom a is updated. The key parameter is a ~String~ that is used to identify the watch and remove it later.

Every time the function f is invoked, it will recieve the following params:

• state: current state of the atom, after the update.
• oldState: the previous state of the atom, before the update. It is possible that state === oldState if you don't update the atom's state or if you update the state in place. The function f is called every time one of the update methods are called, there is no guarantee that the state has actually changed and that the changes are preserved in oldState. That is up to you.
• key: the key provided when adding the watch.
• meta: the metadata provided when performing the update with mreset or mswap. If the update was done through reset or swap this parameter will be undefined.

a.removeWatch(key)

Stop invoking the function for the watch with the key key.