TypeError: Undefined: Redux 4
Redux 4 > createStore > compose The Error TypeError: Cannot read property 'apply' of undefined [ node_modules/redux/es/redux.js:523 ] The Problem and Solution If you've gone through a tutorial in which they suggest adding the Redux Dev Tools in your store.js like this: window.__REDUX_DEVTOOLS_EXTENSION__ && window.__REDUX_DEVTOOLS_EXTENSION__() But they're using it inside of a compose() , you could receive a Type Error for an undefined when the extension is not enabled (or present). The correct way to implement the Redux Dev Tools within a compose is as follows: window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__ || compose I learned this the hard way, and was eventually brought rescue from GitHub user [zalmoxisus] . zalmoxisus also references the docs for this: [ 1.2 Advanced store setup (middleware and enhancers) ] Code Extract from [ store.js ]