warn user when using minified code outside of NODE_ENV 'production'

src/index.js

@@ -3,6 +3,16 @@ import combineReducers from './utils/combineReducers'
 import bindActionCreators from './utils/bindActionCreators'
 import applyMiddleware from './utils/applyMiddleware'
 import compose from './utils/compose'
+import isMinifiedOutsideOfProduction from './utils/isMinifiedOutsideOfProduction'
+
+if (isMinifiedOutsideOfProduction()) {
+  var warningMessage = 'You are utilzing minified code outside of NODE_ENV === \'production\'. ' + 
+    'This means that you are running a slower development only build of Redux. ' + 
+    'Consult tools such as loose-envify (https://github.com/zertosh/loose-envify) for browserify ' + 
+    'and DefinePlugin for webpack (http://stackoverflow.com/questions/30030031) ' + 
+    'to build with proper NODE_ENV'
+  console.error(warningMessage) // eslint-disable-line  no-console
+}
 
 export {
   createStore,

src/utils/isMinifiedOutsideOfProduction.js

@@ -0,0 +1,20 @@
+ /**
+ * This is a function that exists for the function isMinifiedOutsideOfProduction to perform a check.
+ * If this function does not maintain its name and the NODE_ENV is not === 'production'
+ * then we know the user is using minified code outside of production and we should warn
+ *
+ * @returns {Boolean} returns true, is a function that just exists for purpose of checking minifcation
+ */
+function isCrushed() {
+  return true
+}
+/**
+ * Function that checks name of isCrushed and NODE_ENV 
+ * to determine if code is minified outside of production
+ *
+ * @returns {Boolean} A boolean value that is based on whether or not code 
+ * has been minifed outside side of NODE_ENV === 'production'
+ */
+export default function isMinifiedOutsideOfProduction() {
+  return isCrushed.name !== 'isCrushed' && process.env.NODE_ENV !== 'production'
+}