feat: checkContext type narrowing (#28)

fratzinger · web-flow · commit 66d74ea3fa1c · 2026-03-11T15:09:25.000+01:00
* feat: checkContext type narrowing

* fix: checkContext better error message
diff --git a/.claude/settings.json b/.claude/settings.json
@@ -6,7 +6,8 @@
       "Bash(npx vitest typecheck *)",
       "Bash(npx vitepress *)",
       "Bash(npx prettier *)",
-      "Bash(pnpm test)"
+      "Bash(pnpm test)",
+      "Bash(npx eslint *)"
     ]
   }
 }
diff --git a/docs/migrating-from-feathers-hooks-common.md b/docs/migrating-from-feathers-hooks-common.md
@@ -46,6 +46,46 @@ The old `cache` hook only worked for `get` requests and did not work with varyin
 
 The new `cache` hook caches `get` and `find` requests and considers the `params` object when caching. This means that if you call the same `get` or `find` request with different `params`, it will cache each unique request separately.
 
+## `checkContext`
+
+The `checkContext` utility has been updated with an options object syntax and now supports **TypeScript type narrowing**. After calling `checkContext`, the compiler automatically narrows `context.type`, `context.method`, and `context.path` based on the options you pass.
+
+The old positional arguments still work but the options object is recommended:
+
+```ts
+// old
+import { checkContext } from "feathers-hooks-common";
+
+checkContext(context, "before", ["create", "patch"], "myHook");
+
+// new (recommended: options object with type narrowing)
+import { checkContext } from "feathers-utils/utils";
+
+checkContext(context, {
+  type: "before",
+  method: ["create", "patch"],
+  label: "myHook",
+});
+
+// After checkContext, TypeScript narrows the types:
+context.type; // 'before'
+context.method; // 'create' | 'patch'
+```
+
+You can also narrow by `path`, which was not available in the old API:
+
+```ts
+checkContext(context, {
+  type: ["before", "around"],
+  method: ["create", "patch"],
+  path: "users",
+});
+
+context.type; // 'before' | 'around'
+context.method; // 'create' | 'patch'
+context.path; // 'users'
+```
+
 ## `callingParams`
 
 The `callingParams` utility was removed. If you need it please reach out to us in this [github issue](https://github.com/feathersjs/feathers-utils/issues/1).
diff --git a/src/internal.utils.ts b/src/internal.utils.ts
@@ -8,6 +8,7 @@ export const hasOwnProperty = (
 }
 
 export type MaybeArray<T> = T | readonly T[]
+export type UnpackMaybeArray<T> = T extends readonly (infer E)[] ? E : T
 export const toArray = <T>(value: T | readonly T[]): T[] =>
   Array.isArray(value) ? [...value] : [value as T]
 
diff --git a/src/utils/check-context/check-context.util.test-d.ts b/src/utils/check-context/check-context.util.test-d.ts
@@ -22,51 +22,108 @@ type App = typeof app
 type AppCtx = HookContext<App>
 type UserCtx = HookContext<App, MemoryService<User>>
 
-const context = {} as UserCtx
-const appContext = {} as AppCtx
-
 it('options overload accepts valid options', () => {
-  checkContext(context, { type: 'before' })
-  checkContext(context, { method: 'create' })
-  checkContext(context, {
+  const ctx1 = {} as UserCtx
+  checkContext(ctx1, { type: 'before' })
+  const ctx2 = {} as UserCtx
+  checkContext(ctx2, { method: 'create' })
+  const ctx3 = {} as UserCtx
+  checkContext(ctx3, {
     type: ['before', 'around'],
     method: ['create', 'patch'],
   })
-  checkContext(context, { type: 'before', label: 'myHook' })
-  checkContext(context, { path: 'users' })
+  const ctx4 = {} as UserCtx
+  checkContext(ctx4, { type: 'before', label: 'myHook' })
+  const ctx5 = {} as UserCtx
+  checkContext(ctx5, { path: 'users' })
 })
 
 it('options overload rejects invalid type', () => {
+  const ctx = {} as UserCtx
   // @ts-expect-error "invalid" is not a valid HookType
-  checkContext(context, { type: 'invalid' })
+  checkContext(ctx, { type: 'invalid' })
 })
 
 it('options overload accepts valid path for app-level context', () => {
-  checkContext(appContext, { path: 'users' })
-  checkContext(appContext, { path: 'messages' })
-  checkContext(appContext, { path: ['users', 'messages'] })
+  const ctx1 = {} as AppCtx
+  checkContext(ctx1, { path: 'users' })
+  const ctx2 = {} as AppCtx
+  checkContext(ctx2, { path: 'messages' })
+  const ctx3 = {} as AppCtx
+  checkContext(ctx3, { path: ['users', 'messages'] })
 })
 
 it('options overload rejects invalid path for service-specific context', () => {
+  const ctx = {} as UserCtx
   // @ts-expect-error "messages" is not valid when context is narrowed to MemoryService<User>
-  checkContext(context, { path: 'messages' })
+  checkContext(ctx, { path: 'messages' })
 })
 
 it('options overload rejects invalid path for app-level context', () => {
+  const ctx = {} as AppCtx
   // @ts-expect-error "nonExistent" is not a valid service path
-  checkContext(appContext, { path: 'nonExistent' })
+  checkContext(ctx, { path: 'nonExistent' })
 })
 
 it('positional overload accepts valid args', () => {
-  checkContext(context, 'before')
-  checkContext(context, ['before', 'after'])
-  checkContext(context, 'before', 'create')
-  checkContext(context, ['before', 'around'], ['create', 'patch'], 'myHook')
-  checkContext(context, null, 'create')
-  checkContext(context, undefined, 'create')
+  const ctx1 = {} as UserCtx
+  checkContext(ctx1, 'before')
+  const ctx2 = {} as UserCtx
+  checkContext(ctx2, ['before', 'after'])
+  const ctx3 = {} as UserCtx
+  checkContext(ctx3, 'before', 'create')
+  const ctx4 = {} as UserCtx
+  checkContext(ctx4, ['before', 'around'], ['create', 'patch'], 'myHook')
+  const ctx5 = {} as UserCtx
+  checkContext(ctx5, null, 'create')
+  const ctx6 = {} as UserCtx
+  checkContext(ctx6, undefined, 'create')
 })
 
 it('positional overload rejects invalid type', () => {
   // @ts-expect-error "invalid" is not a valid HookType
   checkContext(context, 'invalid')
 })
+
+it('narrows path with options overload', () => {
+  const ctx = {} as AppCtx
+  checkContext(ctx, { path: ['users', 'messages'] })
+  expectTypeOf(ctx.path).toEqualTypeOf<'users' | 'messages'>()
+})
+
+it('narrows path with single value', () => {
+  const ctx = {} as AppCtx
+  checkContext(ctx, { path: 'users' })
+  expectTypeOf(ctx.path).toEqualTypeOf<'users'>()
+})
+
+it('narrows type with options overload', () => {
+  const ctx = {} as AppCtx
+  checkContext(ctx, { type: ['before', 'around'] })
+  expectTypeOf(ctx.type).toEqualTypeOf<'before' | 'around'>()
+})
+
+it('narrows method with options overload', () => {
+  const ctx = {} as AppCtx
+  checkContext(ctx, { method: ['create', 'patch'] })
+  expectTypeOf(ctx.method).toEqualTypeOf<'create' | 'patch'>()
+})
+
+it('narrows type with positional overload', () => {
+  const ctx = {} as AppCtx
+  checkContext(ctx, 'before')
+  expectTypeOf(ctx.type).toEqualTypeOf<'before'>()
+})
+
+it('narrows type and method with positional overload', () => {
+  const ctx = {} as AppCtx
+  checkContext(ctx, ['before', 'around'], ['create', 'patch'])
+  expectTypeOf(ctx.type).toEqualTypeOf<'before' | 'around'>()
+  expectTypeOf(ctx.method).toEqualTypeOf<'create' | 'patch'>()
+})
+
+it('does not narrow when null is passed in positional overload', () => {
+  const ctx = {} as AppCtx
+  checkContext(ctx, null, 'create')
+  expectTypeOf(ctx.method).toEqualTypeOf<'create'>()
+})
diff --git a/src/utils/check-context/check-context.util.test.ts b/src/utils/check-context/check-context.util.test.ts
@@ -164,13 +164,29 @@ describe('util checkContext', () => {
           type: 'before',
           label: 'myHook',
         }),
-      ).toThrow("The 'myHook' hook has invalid context.")
+      ).toThrow(
+        "The 'myHook' hook has invalid context (type: expected 'before' but got 'after').",
+      )
     })
 
     it('uses default label when not provided', () => {
       expect(() =>
         checkContext(make('after', 'create'), { type: 'before' }),
-      ).toThrow("The 'anonymous' hook has invalid context.")
+      ).toThrow(
+        "The 'anonymous' hook has invalid context (type: expected 'before' but got 'after').",
+      )
+    })
+
+    it('shows multiple mismatches in error message', () => {
+      expect(() =>
+        checkContext(make('after', 'patch'), {
+          type: ['before', 'around'],
+          method: 'create',
+          label: 'myHook',
+        }),
+      ).toThrow(
+        "The 'myHook' hook has invalid context (type: expected 'before' | 'around' but got 'after', method: expected 'create' but got 'patch').",
+      )
     })
   })
 })
diff --git a/src/utils/check-context/check-context.util.ts b/src/utils/check-context/check-context.util.ts
@@ -4,6 +4,24 @@ import {
   isContext,
   type IsContextOptions,
 } from '../../predicates/is-context/is-context.predicate.js'
+import type { UnpackMaybeArray } from '../../internal.utils.js'
+
+type NarrowedContext<H extends HookContext, O> = H &
+  (O extends { path: infer P }
+    ? [P] extends [undefined | null]
+      ? unknown
+      : { path: UnpackMaybeArray<P> }
+    : unknown) &
+  (O extends { type: infer T }
+    ? [T] extends [undefined | null]
+      ? unknown
+      : { type: UnpackMaybeArray<T> }
+    : unknown) &
+  (O extends { method: infer M }
+    ? [M] extends [undefined | null]
+      ? unknown
+      : { method: UnpackMaybeArray<M> }
+    : unknown)
 
 export type CheckContextOptions<H extends HookContext = HookContext> =
   IsContextOptions<H> & {
@@ -14,6 +32,7 @@ export type CheckContextOptions<H extends HookContext = HookContext> =
  * Validates that the hook context matches the expected type(s) and method(s).
  * Throws an error if the context is invalid, preventing hooks from running in
  * unsupported configurations. Typically used internally by other hooks.
+ * Also narrows the context type based on the passed options.
  *
  * @example
  * ```ts
@@ -23,22 +42,26 @@ export type CheckContextOptions<H extends HookContext = HookContext> =
  *   checkContext(context, ['before', 'around'], ['create', 'patch'], 'myHook')
  *   // or with options object:
  *   checkContext(context, { type: ['before', 'around'], method: ['create', 'patch'], label: 'myHook' })
- *   // ... hook logic
+ *   // context.type is now 'before' | 'around', context.method is now 'create' | 'patch'
  * }
  * ```
  *
  * @see https://utils.feathersjs.com/utils/check-context.html
  */
-export function checkContext<H extends HookContext = HookContext>(
+export function checkContext<
+  H extends HookContext,
+  const O extends CheckContextOptions<NoInfer<H>>,
+>(context: H, options: O): asserts context is NarrowedContext<H, O>
+export function checkContext<
+  H extends HookContext,
+  const T extends HookType | HookType[] | null | undefined = undefined,
+  const M extends MethodName | MethodName[] | null | undefined = undefined,
+>(
   context: H,
-  options: CheckContextOptions<NoInfer<H>>,
-): void
-export function checkContext<H extends HookContext = HookContext>(
-  context: H,
-  type?: HookType | HookType[] | null,
-  methods?: MethodName | MethodName[] | null,
+  type?: T,
+  methods?: M,
   label?: string,
-): void
+): asserts context is NarrowedContext<H, { type: T; method: M }>
 export function checkContext<H extends HookContext = HookContext>(
   context: H,
   typeOrOptions?:
@@ -69,6 +92,26 @@ export function checkContext<H extends HookContext = HookContext>(
   }
 
   if (!isContext(options)(context)) {
-    throw new Error(`The '${hookLabel}' hook has invalid context.`)
+    const details: string[] = []
+
+    if (options.type != null) {
+      details.push(
+        `type: expected '${Array.isArray(options.type) ? options.type.join("' | '") : options.type}' but got '${context.type}'`,
+      )
+    }
+    if (options.method != null) {
+      details.push(
+        `method: expected '${Array.isArray(options.method) ? options.method.join("' | '") : options.method}' but got '${context.method}'`,
+      )
+    }
+    if (options.path != null) {
+      details.push(
+        `path: expected '${Array.isArray(options.path) ? options.path.join("' | '") : options.path}' but got '${context.path}'`,
+      )
+    }
+
+    throw new Error(
+      `The '${hookLabel}' hook has invalid context (${details.join(', ')}).`,
+    )
   }
 }

Original file line number	Diff line number	Diff line change
`@@ -6,7 +6,8 @@`
`6`	`6`	`"Bash(npx vitest typecheck *)",`
`7`	`7`	`"Bash(npx vitepress *)",`
`8`	`8`	`"Bash(npx prettier *)",`
`9`		`- "Bash(pnpm test)"`
	`9`	`+ "Bash(pnpm test)",`
	`10`	`+ "Bash(npx eslint *)"`
`10`	`11`	`]`
`11`	`12`	`}`
`12`	`13`	`}`
Original file line number	Diff line number	Diff line change
`@@ -8,6 +8,7 @@ export const hasOwnProperty = (`
`8`	`8`	`}`
`9`	`9`
`10`	`10`	`export type MaybeArray<T> = T \| readonly T[]`
	`11`	`+export type UnpackMaybeArray<T> = T extends readonly (infer E)[] ? E : T`
`11`	`12`	`export const toArray = <T>(value: T \| readonly T[]): T[] =>`
`12`	`13`	`Array.isArray(value) ? [...value] : [value as T]`
`13`	`14`