Restrict context to object or undefined

packages/core/src/Machine.ts

@@ -3,30 +3,31 @@ import {
   MachineConfig,
   EventObject,
   AnyEventObject,
-  Typestate
+  Typestate,
+  MachineContext
 } from './types';
 import { StateMachine } from './StateMachine';
 import { Model, ModelContextFrom, ModelEventsFrom } from './model';
 
 export function createMachine<
   TModel extends Model<any, any, any>,
-  TContext = ModelContextFrom<TModel>,
+  TContext extends MachineContext = ModelContextFrom<TModel>,
   TEvent extends EventObject = ModelEventsFrom<TModel>,
   TTypestate extends Typestate<TContext> = { value: any; context: TContext }
 >(
   config: MachineConfig<TContext, TEvent>,
   options?: Partial<MachineImplementations<TContext, TEvent>>
 ): StateMachine<TContext, TEvent, TTypestate>;
 export function createMachine<
-  TContext,
+  TContext extends MachineContext,
   TEvent extends EventObject = AnyEventObject,
   TTypestate extends Typestate<TContext> = { value: any; context: TContext }
 >(
   config: MachineConfig<TContext, TEvent>,
   options?: Partial<MachineImplementations<TContext, TEvent>>
 ): StateMachine<TContext, TEvent, TTypestate>;
 export function createMachine<
-  TContext,
+  TContext extends MachineContext,
   TEvent extends EventObject = AnyEventObject,
   TTypestate extends Typestate<TContext> = { value: any; context: TContext }
 >(

packages/core/src/interpreter.ts

@@ -2,7 +2,6 @@ import {
   Event,
   EventObject,
   CancelActionObject,
-  DefaultContext,
   ActionObject,
   SpecialTargets,
   ActionTypes,
@@ -846,7 +845,7 @@ export class Interpreter<
  * @param options Interpreter options
  */
 export function interpret<
-  TContext = DefaultContext,
+  TContext,
   TEvent extends EventObject = EventObject,
   TTypestate extends Typestate<TContext> = { value: any; context: TContext }
 >(

packages/core/src/model.ts

@@ -4,7 +4,8 @@ import type {
   Assigner,
   PropertyAssigner,
   ExtractEvent,
-  EventObject
+  EventObject,
+  MachineContext
 } from './types';
 import { mapValues } from './utils';
 
@@ -85,11 +86,12 @@ type EventFromEventCreators<EventCreators> = {
     : never;
 }[keyof EventCreators];
 
-export function createModel<TContext, TEvent extends EventObject>(
-  initialContext: TContext
-): Model<TContext, TEvent, void>;
 export function createModel<
-  TContext,
+  TContext extends MachineContext,
+  TEvent extends EventObject
+>(initialContext: TContext): Model<TContext, TEvent, void>;
+export function createModel<
+  TContext extends MachineContext,
   TModelCreators extends ModelCreators<TModelCreators>,
   TFinalModelCreators = FinalModelCreators<TModelCreators>
 >(

packages/core/src/types.ts

@@ -38,7 +38,7 @@ export interface ActionObject<TContext, TEvent extends EventObject> {
   [other: string]: any;
 }
 
-export type DefaultContext = Record<string, any> | undefined;
+export type MachineContext = object | undefined;
 
 /**
  * The specified string event types or the specified event objects.

packages/core/test/actions.test.ts

@@ -1003,7 +1003,7 @@ describe('purely defined actions', () => {
 
 describe('forwardTo()', () => {
   it('should forward an event to a service', (done) => {
-    const child = createMachine<void, { type: 'EVENT'; value: number }>({
+    const child = createMachine<undefined, { type: 'EVENT'; value: number }>({
       id: 'child',
       initial: 'active',
       states: {
@@ -1048,7 +1048,7 @@ describe('forwardTo()', () => {
   });
 
   it('should forward an event to a service (dynamic)', (done) => {
-    const child = createMachine<void, { type: 'EVENT'; value: number }>({
+    const child = createMachine<undefined, { type: 'EVENT'; value: number }>({
       id: 'child',
       initial: 'active',
       states: {

packages/core/test/invoke.test.ts

@@ -492,7 +492,7 @@ describe('invoke', () => {
 
   it('should start services (machine as invoke config)', (done) => {
     const machineInvokeMachine = createMachine<
-      void,
+      undefined,
       { type: 'SUCCESS'; data: number }
     >({
       id: 'machine-invoke',
@@ -532,7 +532,7 @@ describe('invoke', () => {
 
   it('should start deeply nested service (machine as invoke config)', (done) => {
     const machineInvokeMachine = createMachine<
-      void,
+      undefined,
       { type: 'SUCCESS'; data: number }
     >({
       id: 'parent',

packages/core/test/types.test.ts

@@ -1,5 +1,6 @@
 import { assign, createMachine, interpret } from '../src/index';
 import { raise } from '../src/actions';
+import { createModel } from '../src/model';
 
 function noop(_x) {
   return;
@@ -297,3 +298,17 @@ describe('Typestates', () => {
     expect(failed).toEqual({ result: none, error: 'oops' });
   });
 });
+
+describe('types', () => {
+  it('defined context in createMachine() should be an object', () => {
+    createMachine({
+      // @ts-expect-error
+      context: 'string'
+    });
+  });
+
+  it('defined context passed to createModel() should be an object', () => {
+    // @ts-expect-error
+    createModel('string');
+  });
+});

packages/xstate-graph/src/graph.ts

@@ -1,7 +1,7 @@
 import {
   StateNode,
   State,
-  DefaultContext,
+  MachineContext,
   Event,
   EventObject,
   AnyEventObject,
@@ -100,7 +100,7 @@ function getValueAdjMapOptions<TContext, TEvent extends EventObject>(
 }
 
 export function getAdjacencyMap<
-  TContext = DefaultContext,
+  TContext = MachineContext,
   TEvent extends EventObject = AnyEventObject
 >(
   node: MachineNode<TContext, TEvent>,
@@ -170,7 +170,7 @@ export function getAdjacencyMap<
 }
 
 export function getShortestPaths<
-  TContext = DefaultContext,
+  TContext = MachineContext,
   TEvent extends EventObject = EventObject
 >(
   machine: MachineNode<TContext, TEvent>,
@@ -259,7 +259,7 @@ export function getShortestPaths<
 }
 
 export function getSimplePaths<
-  TContext = DefaultContext,
+  TContext = MachineContext,
   TEvent extends EventObject = EventObject
 >(
   machine: MachineNode<TContext, TEvent>,
@@ -332,7 +332,7 @@ export function getSimplePaths<
 }
 
 export function getSimplePathsAsArray<
-  TContext = DefaultContext,
+  TContext = MachineContext,
   TEvent extends EventObject = EventObject
 >(
   machine: MachineNode<TContext, TEvent>,

packages/xstate-test/test/index.test.ts

@@ -395,7 +395,7 @@ describe('events', () => {
       | { type: 'CLOSE' }
       | { type: 'ESC' }
       | { type: 'SUBMIT'; value: string };
-    const feedbackMachine = createMachine<void, Events>({
+    const feedbackMachine = createMachine<undefined, Events>({
       id: 'feedback',
       initial: 'question',
       states: {