avoid relying on this in createSlice

Author: EskiMojo14

packages/toolkit/src/createSlice.ts

@@ -88,22 +88,21 @@ export interface Slice<
   /**
    * Get localised slice selectors (expects to be called with *just* the slice's state as the first parameter)
    */
-  getSelectors(this: this): Id<SliceDefinedSelectors<State, Selectors, State>>
+  getSelectors(): Id<SliceDefinedSelectors<State, Selectors, State>>
 
   /**
    * Get globalised slice selectors (`selectState` callback is expected to receive first parameter and return slice state)
    */
   getSelectors<RootState>(
-    this: this,
-    selectState: (this: this, rootState: RootState) => State
+    selectState: (rootState: RootState) => State
   ): Id<SliceDefinedSelectors<State, Selectors, RootState>>
 
   /**
    * Selectors that assume the slice's state is `rootState[slice.reducerPath]` (which is usually the case)
    *
    * Equivalent to `slice.getSelectors((state: RootState) => state[slice.reducerPath])`.
    */
-  selectors: Id<
+  get selectors(): Id<
     SliceDefinedSelectors<State, Selectors, { [K in ReducerPath]: State }>
   >
 
@@ -126,7 +125,7 @@ export interface Slice<
    *
    * Will throw an error if slice is not found.
    */
-  selectSlice(this: this, state: { [K in ReducerPath]: State }): State
+  selectSlice(state: { [K in ReducerPath]: State }): State
 }
 
 /**
@@ -153,15 +152,15 @@ interface InjectedSlice<
    * Get globalised slice selectors (`selectState` callback is expected to receive first parameter and return slice state)
    */
   getSelectors<RootState>(
-    selectState: (this: this, rootState: RootState) => State | undefined
+    selectState: (rootState: RootState) => State | undefined
   ): Id<SliceDefinedSelectors<State, Selectors, RootState>>
 
   /**
    * Selectors that assume the slice's state is `rootState[slice.name]` (which is usually the case)
    *
    * Equivalent to `slice.getSelectors((state: RootState) => state[slice.name])`.
    */
-  selectors: Id<
+  get selectors(): Id<
     SliceDefinedSelectors<
       State,
       Selectors,
@@ -740,8 +739,8 @@ export function buildCreateSlice({ creators }: BuildCreateSliceConfig = {}) {
 
     const selectSelf = (state: State) => state
 
-    const injectedSelectorCache = new WeakMap<
-      Slice<State, CaseReducers, Name, ReducerPath, Selectors>,
+    const injectedSelectorCache = new Map<
+      string,
       WeakMap<
         (rootState: any) => State | undefined,
         Record<string, (rootState: any) => any>
@@ -750,23 +749,42 @@ export function buildCreateSlice({ creators }: BuildCreateSliceConfig = {}) {
 
     let _reducer: ReducerWithInitialState<State>
 
-    const slice: Slice<State, CaseReducers, Name, ReducerPath, Selectors> = {
-      name,
-      reducerPath,
-      reducer(state, action) {
-        if (!_reducer) _reducer = buildReducer()
+    function reducer(state: State | undefined, action: UnknownAction) {
+      if (!_reducer) _reducer = buildReducer()
 
-        return _reducer(state, action)
-      },
-      actions: context.actionCreators as any,
-      caseReducers: context.sliceCaseReducersByName as any,
-      getInitialState() {
-        if (!_reducer) _reducer = buildReducer()
+      return _reducer(state, action)
+    }
 
-        return _reducer.getInitialState()
-      },
-      getSelectors(selectState: (rootState: any) => State = selectSelf) {
-        const selectorCache = emplace(injectedSelectorCache, this, {
+    function getInitialState() {
+      if (!_reducer) _reducer = buildReducer()
+
+      return _reducer.getInitialState()
+    }
+
+    function makeSelectorProps(
+      reducerPath: ReducerPath,
+      injected = false
+    ): Pick<
+      Slice<State, CaseReducers, Name, ReducerPath, Selectors>,
+      'getSelectors' | 'selectors' | 'selectSlice' | 'reducerPath'
+    > {
+      function selectSlice(state: { [K in ReducerPath]: State }) {
+        let sliceState = state[reducerPath]
+        if (typeof sliceState === 'undefined') {
+          if (injected) {
+            sliceState = getInitialState()
+          } else if (process.env.NODE_ENV !== 'production') {
+            throw new Error(
+              'selectSlice returned undefined for an uninjected slice reducer'
+            )
+          }
+        }
+        return sliceState
+      }
+      function getSelectors(
+        selectState: (rootState: any) => State = selectSelf
+      ) {
+        const selectorCache = emplace(injectedSelectorCache, reducerPath, {
           insert: () => new WeakMap(),
         })
 
@@ -777,39 +795,39 @@ export function buildCreateSlice({ creators }: BuildCreateSliceConfig = {}) {
               options.selectors ?? {}
             )) {
               map[name] = wrapSelector(
-                this,
+                { getInitialState },
                 selector,
                 selectState,
-                this !== slice
+                injected
               )
             }
             return map
           },
         }) as any
-      },
-      selectSlice(state) {
-        let sliceState = state[this.reducerPath]
-        if (typeof sliceState === 'undefined') {
-          // check if injectInto has been called
-          if (this !== slice) {
-            sliceState = this.getInitialState()
-          } else if (process.env.NODE_ENV !== 'production') {
-            throw new Error(
-              'selectSlice returned undefined for an uninjected slice reducer'
-            )
-          }
-        }
-        return sliceState
-      },
-      get selectors() {
-        return this.getSelectors(this.selectSlice)
-      },
+      }
+      return {
+        reducerPath,
+        getSelectors,
+        get selectors() {
+          return getSelectors(selectSlice)
+        },
+        selectSlice,
+      }
+    }
+
+    const slice: Slice<State, CaseReducers, Name, ReducerPath, Selectors> = {
+      name,
+      reducer,
+      actions: context.actionCreators as any,
+      caseReducers: context.sliceCaseReducersByName as any,
+      getInitialState,
+      ...makeSelectorProps(reducerPath),
       injectInto(injectable, { reducerPath: pathOpt, ...config } = {}) {
-        const reducerPath = pathOpt ?? this.reducerPath
-        injectable.inject({ reducerPath, reducer: this.reducer }, config)
+        const newReducerPath = pathOpt ?? reducerPath
+        injectable.inject({ reducerPath: newReducerPath, reducer }, config)
         return {
-          ...this,
-          reducerPath,
+          ...slice,
+          ...makeSelectorProps(newReducerPath as any, true),
         } as any
       },
     }
@@ -818,13 +836,13 @@ export function buildCreateSlice({ creators }: BuildCreateSliceConfig = {}) {
 }
 
 function wrapSelector<State, NewState, S extends Selector<State>>(
-  slice: Slice,
+  slice: { getInitialState(): State },
   selector: S,
   selectState: Selector<NewState, State>,
   injected?: boolean
 ) {
   function wrapper(rootState: NewState, ...args: any[]) {
-    let sliceState = selectState.call(slice, rootState)
+    let sliceState = selectState(rootState)
     if (typeof sliceState === 'undefined') {
       if (injected) {
         sliceState = slice.getInitialState()

packages/toolkit/src/tests/createSlice.test.ts

@@ -493,6 +493,16 @@ describe('createSlice', () => {
     it('allows accessing properties on the selector', () => {
       expect(slice.selectors.selectMultiple.unwrapped.test).toBe(0)
     })
+    it('has selectSlice attached to slice, which can go without this', () => {
+      const slice = createSlice({
+        name: 'counter',
+        initialState: 42,
+        reducers: {},
+      })
+      const { selectSlice } = slice
+      expect(() => selectSlice({ counter: 42 })).not.toThrow()
+      expect(selectSlice({ counter: 42 })).toBe(42)
+    })
   })
   describe('slice injections', () => {
     it('uses injectInto to inject slice into combined reducer', () => {