Inline the symbol-observable polyfill

index.d.ts

@@ -1,5 +1,3 @@
-/// <reference types="symbol-observable" />
-
 /**
  * An *action* is a plain object that represents an intention to change the
  * state. Actions are the only way to get data into the store. Any data,
@@ -224,6 +222,12 @@ export interface Unsubscribe {
   (): void
 }
 
+declare global {
+  interface SymbolConstructor {
+    readonly observable: symbol;
+  }
+}
+
 /**
  * A minimal observable of state changes.
  * For more information, see the observable proposal:

src/createStore.js

@@ -1,4 +1,4 @@
-import $$observable from 'symbol-observable'
+import $$observable from './utils/symbol-observable'
 
 import ActionTypes from './utils/actionTypes'
 import isPlainObject from './utils/isPlainObject'

src/utils/symbol-observable.js

@@ -0,0 +1,3 @@
+// Inlined version of the `symbol-observable` polyfill
+export default (() =>
+  (typeof Symbol === 'function' && Symbol.observable) || '@@observable')()

test/createStore.spec.js

@@ -11,13 +11,16 @@ import {
 import * as reducers from './helpers/reducers'
 import { from } from 'rxjs'
 import { map } from 'rxjs/operators'
-import $$observable from 'symbol-observable'
+import $$observable from '../src/utils/symbol-observable'
 
 describe('createStore', () => {
   it('exposes the public API', () => {
     const store = createStore(combineReducers(reducers))
-    const methods = Object.keys(store)
 
+    // Since switching to internal Symbol.observable impl, it will show up as a key in node env
+    // So we filter it out
+    const methods = Object.keys(store).filter(key => key !== $$observable)
+
     expect(methods.length).toBe(4)
     expect(methods).toContain('subscribe')
     expect(methods).toContain('dispatch')

test/typescript/store.ts

@@ -9,7 +9,8 @@ import {
   Unsubscribe,
   Observer,
 } from 'redux'
-import 'symbol-observable'
+// @ts-ignore
+import $$observable from '../src/utils/symbol-observable'
 
 type BrandedString = string & { _brand: 'type' }
 const brandedString = 'a string' as BrandedString