Troubleshooting Effector

Common Errors

store: undefined is used to skip updates. To allow undefined as a value provide explicit { skipVoid: false } option

This error indicates that you are trying to pass undefined as a value to your store, which might not be the intended behavior.

If you really need to store undefined, pass an object with { skipVoid: false } as the second argument to createStore:

const $store = createStore(0, {
  skipVoid: false,
});

no handler used in [effect name]

This error occurs when calling an effect without a handler. Make sure you passed a handler to the createEffect method during creation, or later when using the .use(handler) method.

serialize: One or more stores dont have sids, their values are omitted

This error commonly occurs in SSR scenarios due to the absence of an sid (stable id), which is required for proper hydration of store data from the server to the client.

To fix this, add an sid to your store. You can do this in one of the following ways:

1. Use the Babel or SWC plugin to handle it automatically.

2. Manually specify an sid by providing an object with a sid property as the second argument to createStore:

   const $store = createStore(0, {
     sid: "unique id",
   });

For more details, see Understanding sid and its purpose.

scopeBind: scope not found

This error occurs when a scope is lost at some point in execution, preventing scopeBind from associating an event or effect with the correct execution scope.
It may be caused by:

1. Using a “scope-free” mode where scopes are not present in your application.
2. Calling units outside of a scope.

Possible Solutions:

1. Ensure scopeBind is used within effects:

   const event = createEvent();
   
   // ❌ - Do not call scopeBind inside callbacks
   const effectFx = createEffect(() => {
     setTimeout(() => {
       scopeBind(event)();
     }, 1111);
   });
   
   // ✅ - Use scopeBind inside the effect
   const effectFx = createEffect(() => {
     const scopeEvent = scopeBind(event);
   
     setTimeout(() => {
       scopeEvent();
     }, 1111);
   });

2. Ensure that your units are used inside a scope:

   • When working with a framework, use useUnit.
   • If calling an event or effect outside a framework, use allSettled and provide the appropriate scope as an argument.

If necessary, and you want to suppress the error, you can pass { safe: true } as an option:

const scopeEvent = scopeBind(event, {
  safe: true,
});

call of derived event is not supported, use createEvent instead

This error occurs when you try to call a derived event as a function. Derived events are created by methods like .map(), .filter(), .filterMap(), as well as the sample operator.

To fix this, use an event created via createEvent.

unit call from pure function is not supported, use operators like sample instead

This error occurs when you try to call events or effects from pure functions in Effector:

• Calling events in event methods
  When you try to call one event inside another event’s .map(), .filter(), .filterMap(), or .prepend() methods.

• Calling events in store handlers
  When attempting to call an event in a .on() handler, inside the .map() method, or in the updateFilter() configuration property of a store.

• Calling events in sample functions
  When calling an event in the fn or filter function of the sample operator.

How to fix: Instead of calling events in pure functions, use declarative operators, for example, sample.

Gotchas

sample.fn does not narrow the type passed from sample.filter

A common type-related issue with sample occurs when a check is performed in filter, but fn does not receive the correctly narrowed type. To resolve this, you can add type predicates or use the effector-action library, which helps simplify conditional types:

import { sample } from "effector";

const messageSent = createEvent<Message>();
const userText = createEvent<string>();

sample({
  clock: messageSent,
  filter: (msg: Message): msg is UserMessage => msg.kind === "user",
  fn: (msg) => msg.text,
  target: userText,
});

import { createAction } from "effector-action";

const userText = createEvent<string>();

const messageSent = createAction({
  target: userText,
  fn: (userText, msg: Message) => {
    if (msg.kind === "user") {
      userText(msg.txt);
    }
  },
});

My state did not change

If your state does not update as expected, you are likely working with scopes and, at some point, the active scope was lost. As a result, your unit executed in the global scope instead.

Typical places where this happens:

• setTimeout / setInterval
• addEventListener
• WebSocket
• direct promise calls inside effects
• third-party libraries with async APIs or callbacks.

Solution: Bind your event or effect to the current scope using scopeBind:

// ✅ correct way

const event = createEvent();

const effectFx = createEffect(() => {
  const scopedEvent = scopeBind(event);

  setTimeout(() => {
    scopedEvent();
  }, 1000);
});

// ❌ event will execute in the global scope

const event = createEvent();

const effectFx = createEffect(() => {
  setTimeout(() => {
    event();
  }, 1000);
});

Using units without useUnit

If you’re using events or effects in a framework without useUnit, this may also lead to scope loss.
To fix this, pass the unit to the useUnit hook and use the returned value:

// ✅ hook used

import { event } from "./model.js";
import { useUnit } from "effector-react";

const Component = () => {
  const onEvent = useUnit(event);

  return <button onClick={() => onEvent()}>click me</button>;
};

// ❌ direct unit call

import { event } from "./model.js";

const Component = () => {
  return <button onClick={() => event()}>click me</button>;
};

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