spawn-usage.md

Enforce proper usage of the spawn function

Ensure that the spawn function imported from xstate is used correctly.

** This rule is compatible with XState v4 only! **

Rule Details

The spawn function has to be used in the context of an assignment function. Failing to do so creates an orphaned actor which has no effect.

XState v5

XState v5 changed the way the spawn function is accessed. This effectively eliminated the possibility of using the spawn function outside of the assign function. Therefore, this rule becomes obsolete in XState v5. Do not use it with XState v5.

Examples of incorrect code for this rule:

import { spawn } from 'xstate'

// ❌ spawn called outside of a state machine
const someActorRef = spawn(someMachine)

// ❌ spawn is not an action creator
{
  actions: spawn(someMachine)
}

// ❌ spawn called outside of an assignment function
{
  actions: assign({
    // execute in context of the parent machine definition
    someActorRef: spawn(someMachine),
  })
}

Examples of correct code for this rule:

import { spawn } from 'xstate'

// ✅ spawn called lazily inside an object assigner
{
  actions: assign({
    someActorRef: () => spawn(someMachine),
  })
}

// ✅ spawn called inside a function assigner
{
  actions: assign(() => ({
    someActorRef: spawn(someMachine),
  }))
}

Further Reading

• Spawning actors