Understanding redux-thunk

createThunkMiddleware.js

//  createThunkMiddleware from redux-thunk.js
 export function createThunkMiddleware(extraArgument) {
    return function thunkFunction ({ dispatch, getState }) {
      return function nextFunction (next) { 
          console.info("In next function")
          console.dir(next)
         return function actionFunction (action) {
            console.info("action RETURNED")
            console.dir(action)
            
            if (typeof action === 'function') {
              console.info("++++++++++++++++++++++++++++++++++++++")
              console.info("action is function")
              console.info("++++++++++++++++++++++++++++++++++++++")
              return action(dispatch, getState, extraArgument);
            }
            
            console.info("+++++++++++++++++calling NEXT++++++++++++++")
            console.dir(next)
            return next(action);
          }
       }
    }
}

const thunk = createThunkMiddleware();
thunk.withExtraArgument = createThunkMiddleware;

export default thunk