Optics

focusAtom

Takes an atom and creates a writable atom with corresponding focus.

function focusAtom(wholeAtom: WritableAtom, focus: Focus): WritableAtom

const wholeAtom = atom({ a: 2 })
const partAtom = focusAtom(wholeAtom, prop('a'))

const store = createStore()
store.get(partAtom) // 2
store.set(partAtom, 3) // { a: 3 }

viewAtom

function viewAtom(wholeAtom, focus)

Takes an atom and creates a readonly atom with corresponding focus. It is useful when the wholeAtom is either readonly or has a setter type that would not be compatible with focusAtom, such as a machineAtom.

const wholeAtom = atom(1)
const partAtom = wholeAtom(sourceAtom, linear(2))

foldAtom

function foldAtom(wholeAtom: Atom, focus: Focus): ({
    foldFn: (p: Part, acc: Acc) => Acc,
    init: Acc | () => Acc,
}) => Atom

Takes an atom and creates a function taking a FoldForm and returning a readonly atom corresponding to the result of the folding operation.

const odd = (x: number) => x % 2
const wholeAtom = atom([1, 2, 3])
const store = createStore()

const collectAtom = foldAtom(wholeAtom, pipe(elems(), when(odd)))(toArray())
store.get(collectAtom) // [1, 3]

const sumAtom = foldAtom(
	wholeAtom,
	pipe(elems(), when(odd)),
)({
	foldFn: (value, acc) => value + acc,
	init: 0,
})

store.get(sumAtom) // 4

disabledFocusAtom

The setter of the resulting atom takes no parameter and updates wholeAtom according to part and focus.

The getter is a boolean reflecting whether applying the setter would have an effect on the value. We only compare the value in focus before and after applying the value, which avoid the need for deep comparison (but might be misleading with very unlawful optics, such as queue). The default comparison function is shallowEqual.

part can also be the symbol REMOVE (when applicable) or an update function.

This is useful for binding an event with a button-like element, hence the name.

disabledFocusAtom(wholeAtom, focus, part, areEqual?)