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

It is helpful to debug your application's logic.

Just pass any effector's unit to debug.


Sometimes during development, it is necessary to display the value of the stores and payload of events, each time you write console.log inside .watch and copy/paste it is unpleasant. debug allows you to speed up this process a lot by passing all the necessary units for a debugging into a method arguments.


import { createStore, createEvent, createEffect } from 'effector';
import { debug } from 'patronum/debug';

const event = createEvent();
const effect = createEffect().use((payload) => Promise.resolve('result' + payload));
const $store = createStore(0)
.on(event, (state, value) => state + value)
.on(effect.done, (state) => state * 10);

debug($store, event, effect);


// => [store] $store 1
// => [event] event 5
// => [store] $store 6
// => [effect] effect demo
// => [effect] effect.done {"params":"demo", "result": "resultdemo"}
// => [store] $store 60



patronum 1.9.0

patronum/debug supports computation traces logging, if { trace: true } is set. It is recommended to use this feature along with effector/babel-plugin.

const inputChanged = createEvent();
const $form = createStore(0).on(inputChanged, (s) => s + 1);

debug({ trace: true }, $form, submitFx);


// "[store] $form 0",
// "[store] $form 1",
// "[store] $form trace",
// "<- [store] $form 1",
// "<- [$form.on] $form.on(inputChanged) 1",
// "<- [event] inputChanged ",

Custom names

Sometimes unit name in specific context may be different from the one it was initially created with. e.g., an unit may be exported under an alias for explicitness:

export const $productsListVisible = productsPageModel.$open;
const productAdded = createEvent();

debug($productsListVisible, productAdded);
// or
debug({ trace: true }, $productsListVisible, productAdded);

In this case, because of effector/babel-plugin which provided productsPageModel.$open store its name at the moment of its creation, public name in the debug logs will be $open instead of $productsListVisible.

It can be fixed with custom name, which can be provided by using Record<string, Unit> instead of a list of units:

export const $productsListVisible = productsPageModel.$open;
const productAdded = createEvent();

debug({ $productsListVisible, customEventName: productAdded });
// or
debug({ trace: true }, { $productsListVisible, customEventName: productAdded });

This way $productsListVisible name in the logs will be the same, as the one which was provided to debug. The productAdded event will be named customEventName.

Fork API and Scope

Effector can run multiple "instances" of the app simultaniosly via Fork API - it is useful for tests and SSR. Usually you would also use scope on the client in the case of SSR. debug will log "scoped" updates in such case:

const up = createEvent();
const $count = createStore(0).on(up, (s) => s + 1);
const fx = createEffect(() => {});
clock: $count,
target: fx,


const scopeA = fork();

await allSettled(up, { scope: scopeA });

// "[effect] (scope: unknown_scope_3) fx 1",
// "[effect] (scope: unknown_scope_3) fx.done {\\"params\\":1}",

By default detected scope will be given default name.

Scope registration

It is possible to explicitly register scope with given name to have a more explicit logs.

It can work like this:

const scope = fork({ values: window.__SSR_VALUES__ });

// this way we can commit this to our repo and be sure,
// that bundler will cut this out of production bundle
if (process.env.NODE_ENV === 'development') {
debug.registerScope(scope, { name: 'my_client_scope' });

This way scope will be given explicit name in the logs.

// "[effect] (scope: my_client_scope) fx 1",
// "[effect] (scope: my_client_scope) fx.done {\\"params\\":1}",

It is also possible to unregister scope to prevent memory leak, if scope is no longer needed:

const unregister = debug.registerScope(scope, { name: `my_scope` });


Or unregister all scopes at once:


Initial store state

debug($store) always immediately prints current state of the store, but this state can be different in different scopes. It is recommended to register scopes explicitly, since debug will print current state of the store in every known scope:

const $count = createStore(0);

const scopeA = fork({
values: [[$count, 42]],
const scopeB = fork({
values: [[$count, 1337]],

debug.registerScope(scopeA, { name: 'scope_42' });
debug.registerScope(scopeB, { name: 'scope_1337' });


// "[store] $count 0",
// "[store] (scope: scope_42) $count 42",
// "[store] (scope: scope_1337) $count 1337",


The patronum/debug package extracts quite a lot of low-level effector data in a universal format that may be useful for other dev tools or monitoring tools, so there is a special API to add your own way of handling this data.

Custom handler

You can provide custom log handler in the config. It can be useful, if somehow doesn't fit your use-case: e.g. you want advanced info from patronum/debug to built your own dev-tools, debug especially hard case, etc.

Handler is called for each update with context object like this:

Common fields:

  • logType - initial | update - log type for convenience. All provided stores current values are logged with initial for all known scopes right away. Same after new scope was registered. All other updates are of update type.
  • scope - Scope | null - effector's Scope context object, which owns this particular update
  • scopeName - string | null - name of the Scope, if registered and null otherwise.
  • node - Node - effector's internal node, which update is being logged.
  • name - string | null - node's name for convenience. null - if node doesn't have own name (like sample calls).
  • kind - string - node's kind for convenience. It can be unit's kind (e.g. store or event) or operation kind (e.g. sample, split, etc).
  • value - unknown - value of the update.
  • loc - { file?: string; line: number; column: number; } - location in the source code, if known
  • stackMeta - { Record<string, unknown> } - effector's internal stack metadata, available if provided. For example, effect calls provide an fxID that is stable between fx and fx.finally updates - this allows you to associate a fx.finally update with a particular fx call (available since effector@22.5.0)

Special field if trace: true provided:

  • trace - Array<{ node: Node; name: string | null; kind: string; value: unknown; loc?: Loc; stackMeta?: Record<string, unknown> }> - trace of updates.

The trace array is always empty (i.e. trace is not collected), if debug's config does not have trace: true.

trace: true,
// custom log handler
handler: ({ trace, scope, scopeName, node, value, name, kind }) => {
// your own way to log updates
doStuff(node, value);

if (trace) {
// log trace part
trace.forEach(({ name, kind, node, value }) => doStuff(node, value));
{ $a, $b, c },