Atom collections

atomCollection<T>(options) is a thin layer over createAtom that ships array-mutation verbs as actions.

Signature

atomCollection<Value>(options: CollectionOptions<Value>): Atom<Value[], AtomCollectionActions<Value>>

type CollectionOptions<V> = Omit<AtomOptions<V[], AtomCollectionActions<V>>, "default"> & {
  default?: V[];   // defaults to []
};

Actions

Action	Description
`push(...items)`	Append.
`unshift(...items)`	Prepend.
`pop()` / `shift()`	Drop last / first.
`replace(index, item)`	Overwrite at index.
`remove(indexOrPredicate)`	Drop one by index or `(item, index, array) => boolean`.
`removeItem(item)`	Strict-equality remove of the first occurrence.
`removeAll(item)`	Remove every occurrence of `item` (strict equality). Mutates and triggers update.
`map(cb)`	In-place map: rewrites the value AND returns the new array.
`forEach(cb)`	Read-only iteration.
`index(predicate)`	`findIndex` wrapper.
`get(indexOrPredicate)`	Single-element read.
`length`	Property getter — current size.

Example

type Todo = { id: number; text: string; done: boolean };

const todos = atomCollection<Todo>({
  key: "todos",
  default: [],
  actions: {
    toggle(this: Atom<Todo[]>, id: number) {
      this.update(this.value.map(t => t.id === id ? { ...t, done: !t.done } : t));
    },
  },
});

todos.push({ id: 1, text: "Buy bread", done: false });
todos.toggle(1);
todos.remove((t) => t.done);

Gotchas

map is mutating despite the name — it rewrites the value AND returns the new array. Use atom.value.map(...) if you want a pure transform.
The length action is exposed as a property getter, not a function. Read it as todos.length, not todos.length().