Add selector factories to createSlice

packages/toolkit/src/combineSlices.ts

@@ -8,6 +8,7 @@ import type {
   UnionToIntersection,
   WithOptionalProp,
 } from './tsHelpers'
+import { emplace } from './utils'
 
 type SliceLike<ReducerPath extends string, State> = {
   reducerPath: ReducerPath
@@ -330,37 +331,34 @@ const stateProxyMap = new WeakMap<object, object>()
 const createStateProxy = <State extends object>(
   state: State,
   reducerMap: Partial<Record<string, Reducer>>
-) => {
-  let proxy = stateProxyMap.get(state)
-  if (!proxy) {
-    proxy = new Proxy(state, {
-      get: (target, prop, receiver) => {
-        if (prop === ORIGINAL_STATE) return target
-        const result = Reflect.get(target, prop, receiver)
-        if (typeof result === 'undefined') {
-          const reducer = reducerMap[prop.toString()]
-          if (reducer) {
-            // ensure action type is random, to prevent reducer treating it differently
-            const reducerResult = reducer(undefined, { type: nanoid() })
-            if (typeof reducerResult === 'undefined') {
-              throw new Error(
-                `The slice reducer for key "${prop.toString()}" returned undefined when called for selector(). ` +
-                  `If the state passed to the reducer is undefined, you must ` +
-                  `explicitly return the initial state. The initial state may ` +
-                  `not be undefined. If you don't want to set a value for this reducer, ` +
-                  `you can use null instead of undefined.`
-              )
+) =>
+  emplace(stateProxyMap, state, {
+    insert: () =>
+      new Proxy(state, {
+        get: (target, prop, receiver) => {
+          if (prop === ORIGINAL_STATE) return target
+          const result = Reflect.get(target, prop, receiver)
+          if (typeof result === 'undefined') {
+            const reducer = reducerMap[prop.toString()]
+            if (reducer) {
+              // ensure action type is random, to prevent reducer treating it differently
+              const reducerResult = reducer(undefined, { type: nanoid() })
+              if (typeof reducerResult === 'undefined') {
+                throw new Error(
+                  `The slice reducer for key "${prop.toString()}" returned undefined when called for selector(). ` +
+                    `If the state passed to the reducer is undefined, you must ` +
+                    `explicitly return the initial state. The initial state may ` +
+                    `not be undefined. If you don't want to set a value for this reducer, ` +
+                    `you can use null instead of undefined.`
+                )
+              }
+              return reducerResult
             }
-            return reducerResult
           }
-        }
-        return result
-      },
-    })
-    stateProxyMap.set(state, proxy)
-  }
-  return proxy as State
-}
+          return result
+        },
+      }),
+  }) as State
 
 const original = (state: any) => {
   if (!isStateProxy(state)) {