planning

node_modules/redux-thunk/src/index.ts

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+import type { Action, AnyAction } from 'redux'
+
+import type { ThunkMiddleware } from './types'
+
+export type {
+  ThunkAction,
+  ThunkDispatch,
+  ThunkActionDispatch,
+  ThunkMiddleware
+} from './types'
+
+/** A function that accepts a potential "extra argument" value to be injected later,
+ * and returns an instance of the thunk middleware that uses that value
+ */
+function createThunkMiddleware<
+  State = any,
+  BasicAction extends Action = AnyAction,
+  ExtraThunkArg = undefined
+>(extraArgument?: ExtraThunkArg) {
+  // Standard Redux middleware definition pattern:
+  // See: https://redux.js.org/tutorials/fundamentals/part-4-store#writing-custom-middleware
+  const middleware: ThunkMiddleware<State, BasicAction, ExtraThunkArg> =
+    ({ dispatch, getState }) =>
+    next =>
+    action => {
+      // The thunk middleware looks for any functions that were passed to `store.dispatch`.
+      // If this "action" is really a function, call it and return the result.
+      if (typeof action === 'function') {
+        // Inject the store's `dispatch` and `getState` methods, as well as any "extra arg"
+        return action(dispatch, getState, extraArgument)
+      }
+
+      // Otherwise, pass the action down the middleware chain as usual
+      return next(action)
+    }
+  return middleware
+}
+
+const thunk = createThunkMiddleware() as ThunkMiddleware & {
+  withExtraArgument<
+    ExtraThunkArg,
+    State = any,
+    BasicAction extends Action = AnyAction
+  >(
+    extraArgument: ExtraThunkArg
+  ): ThunkMiddleware<State, BasicAction, ExtraThunkArg>
+}
+
+// Attach the factory function so users can create a customized version
+// with whatever "extra arg" they want to inject into their thunks
+thunk.withExtraArgument = createThunkMiddleware
+
+export default thunk