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previous

since

patronum 2.1.0

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

Motivation​

The method allows to get previous value of given store. Usually need for analytics

Formulae​

$target = previous($source);
$target = previous($source, 'initial value');

Arguments​

  1. $source ([Store]) - source store
  2. defaultValue (optional) - default value for $target store, if not passed, null will be used

Returns​

  • $target ([Store]) - new store that contain previous value of $source after first update and null or default value (if passed) before that

Example​

Push analytics with route transition:

import { createStore, createEvent, createEffect, sample } from 'effector';
import { previous } from 'patronum';

const openNewRoute = createEvent<string>();
const $currentRoute = createStore('main_page');
const $previousRoute = previous($currentRoute);

const sendRouteTransitionFx = createEffect(async ({ prevRoute, nextRoute }) => {
  console.log(prevRoute, '->', newRoute)
  await fetch(...)
});

sample({clock: openNewRoute, target: $currentRoute});

sample({
  clock: openNewRoute,
  source: {
    prevRoute: $previousRoute,
    nextRoute: $currentRoute,
  },
  target: sendRouteTransitionFx,
});

openNewRoute('messages');
// main_page -> messages
openNewRoute('chats');
// messages -> chats