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snapshot

since

patronum 1.7.0

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

result = snapshot({ source, clock, fn })​

Motivation​

This method allows to copy any store on optional trigger unit. It useful when you want to save previous state of store before some actions.

Formulae​

result = snapshot({ source, clock, fn });
  • Call fn with data from source while clock triggered, and create store with the value
  • If fn returns undefined, the update will be skipped.

Arguments​

  1. source (Store) — Source store, data from this unit passed to fn
  2. clock (Event, Effect, Store) — Trigger unit
  3. fn ((value: T) => U) — Transformation function

Returns​

  • result (Store) — Copied store

Examples​

Exact copy of store​

import { createStore } from 'effector';
import { snapshot } from 'patronum/snapshot';

const $original = createStore<string>('Example');

const $copy = snapshot({ source: $original });

Exact copy on trigger​

import { restore, createEvent } from 'effector';
import { snapshot } from 'patronum/snapshot';

const changeText = createEvent<string>();
const createSnapshot = createEvent();

const $original = restore(changeText, 'Example');

const $snapshot = snapshot({
  source: $original,
  clock: createSnapshot,
});

changeText('New text');

// $original -> Store with "New text"
// $snapshot -> Store with "Example"

createSnapshot();

// $original -> Store with "New text"
// $snapshot -> Store with "New text"

Copy on trigger with transformation​

import { restore, createEvent } from 'effector';
import { snapshot } from 'patronum/snapshot';

const changeText = createEvent<string>();
const createSnapshot = createEvent();

const $original = restore(changeText, 'Example');

const $lengthSnapshot = snapshot({
  source: $original,
  clock: createSnapshot,
  fn: (text) => text.length,
});

// $original -> Store with "Example"
// $lengthSnapshot -> Store with 7 (length of "Example")

changeText('New long text');

// $original -> Store with "New long text"
// $lengthSnapshot -> Store with 7 (length of "Example")

createSnapshot();

// $original -> Store with "New long text"
// $lengthSnapshot -> Store with 13 (length of "New long text")