API reference

createAtom(initialState, actions, options)

Create an atom.


type: any default: {}

The initial state of the atom.


type: object default: {}

An object with action functions. The signature of an action function is ({ get, set, dispatch }, payload). If you provide nested action objects or other structure, make sure to also specify an appropriate options.evolve implementation to handle your actions appropriately.

  • get() - returns the current state
  • set(patch) - updates the state with the patch object by merging the patch using Object.assign
  • swap(state) - replace the entire state with the provided one
  • dispatch - same as atom.dispatch, dispatches an action


type: function

A function that receives all of the dispatched action objects and calls the action functions. The function signature is (atom, action, actions). Note that atom in this place has an extra added function set, a function that is used to update the state, this function does not exist on the actual atom. The default implementation uses action.type to find the matching function in the actions object.


type: function | function[] default: null

A function that will be called on each action and state update. The function is passed an info object of shape { type, atom, action, sourceActions, prevState }. Tiny atom comes with 2 built in debug functions tiny-atom/log and tiny-atom/devtools.

createAtom({ count: 1 }, {
  increment: ({ get, set }, payload) => set({ count: get().count + payload }),
  inc: ({ dispatch }, payload) => dispatch('increment', payload)


Get current state.



Update current state by merging the update shallowly.

atom.set({ user })
atom.set({ entities: { ...entities, posts } })


Replace the state with the provided one.


atom.dispatch(type, payload)

Send an action

atom.dispatch('increment', 5)


Register a callback for when atom changes. Returns the unobserve function.

atom.observe(atom => render(atom.get(), atom.dispatch))

atom.fuse(state, actions)

Extend atom’s state and the action object. Convenient for composing atom from slices of state and actions from several modules.

const state = {
  project: { name: 'tiny-atom' }

const actions = {
  star: ({ get, set }) => set({
    project: { starred: true }

atom.fuse(state, actions)