empty (experimental)

since

patronum 1.10.0

experimental

Operator is going to be renamed. Please review the discussion.

import { empty } from 'patronum';
// or
import { empty } from 'patronum/empty';

Motivation

The method allows to check passed value for null. Sometimes you need just to check for nullability, and go on.

Formulae

$result = empty($value);

• $result store contains true if $value store contains null

Arguments

• $value: Store<T | null> — The store contains any kind of value.

Returns

• $result: Store<boolean> — The store contains false if passed $value store contains any kind of value other from null

Example

const $account = createStore<Account | null>(null);
const $anonymous = empty($account);
const $authorized = not($anonymous);

console.assert(true === $anonymous.getState());
console.assert(false === $authorized.getState());

Try it

Alternative

import { createStore } from 'effector';
const $account = createStore<Account | null>(null);
const $anonymous = $account.map((account) => account === null);
const $authorized = $anonymous.map((anonymous) => !anonymous);

console.assert(true === $anonymous.getState());
console.assert(false === $authorized.getState());