Merge pull request #1325 from JamieDixon/master

subscribe to throw when listener is not a function

src/createStore.js

@@ -79,6 +79,10 @@ export default function createStore(reducer, initialState, enhancer) {
    * @returns {Function} A function to remove this change listener.
    */
   function subscribe(listener) {
+    if (typeof listener !== 'function') {
+      throw new Error('Expected listener to be a function.')
+    }
+
     listeners.push(listener)
     var isSubscribed = true
 

test/createStore.spec.js

@@ -548,4 +548,24 @@ describe('createStore', () => {
       store.replaceReducer(() => {})
     ).toNotThrow()
   })
+
+  it('throws if listener is not a function', () => {
+    const store = createStore(reducers.todos)
+
+    expect(() =>
+      store.subscribe()
+    ).toThrow()
+
+    expect(() =>
+      store.subscribe('')
+    ).toThrow()
+
+    expect(() =>
+      store.subscribe(null)
+    ).toThrow()
+
+    expect(() =>
+      store.subscribe(undefined)
+    ).toThrow()
+  })
 })