logger.js

const logger => store => next => action => {
  console.log("Logging", param)
  next(action)
}

export default logger;

logger1.js

// This is how our logger middleware will look like without arrow functions
const logger = function(store) {
  return function(next) {
    return function(action) {
      console.log("Logging", param)
      next(action) 
    }
  }
}

// This type of function will be called like this
// logger(store)(next)(action)
// Instead of logger(store, next, action)
// See my article on currying to understand this better.

export default logger;