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0.5.0 • Public • Published

Fraud Redux-Logger

redux-logger with more features

An attempt at implementing redux-logger using Typescript with more features! Seems like redux-logger is not very active. IMHO, there's a lot of disgusting stuff in there :3



Unlike redux-logger, you can fully customize how logging is performed. redux-logger only provides 1 customization point : the options. This library exposes 2 customization points : the printer and the options. Therefore, you can tailor logging to your exact needs. For example, the default logging provided in redux-logger does not really work outside of Chrome's console. If you look at our example in customizedLogger, you can instead just print normally without any formatting.


This library is implemented entirely using TypeScript which makes maintaining and fixing this library much, much easier.

Cleaner code

This is just my opinion, but there's a lot of dubious stuff in the redux-logger. For example, it performs indirection unnecessarily. However, I'll let you be the judge of that :3


To use this library, lets look at the simplest way we can create a logging middleware.

// An empty option class
type CustomOption = {}
const basicPrinter: Printer<TestState, TestError, CustomOption> = {
  // Are we logging exceptions?
  logError: true,
  // If this function returns true, we log. Else, we dont't.
  logPredicate: (s: TestState, b: AnyAction) => true,
  // The logging function.
  printLog: (logEntry: LogEntry<TestState, TestError>, customOption: CustomOption) => {
// Finally apply the middleware.
const store = createStore(
  applyMiddleware(createLogger<TestState, TestError, CustomOption>(basicPrinter, {}))

Notice that this library does not actually perform any logging. However, we do provide sane defaults that works really well on the web that is very similar to redux-logger. However, because you are not bound to our implementation, you can do whatever you want!

Type Signatures

createLogger Function

export const createLogger: <S, E, O>(printer: Printer<S, E, O>, options: O) => MiddlewareFunction<S, Dispatch<AnyAction>, AnyAction> = ...

Quite scary, but lets take a look at it slowly.

  1. S is simply the full state of your application i.e. it is the root reducer of your Redux.
  2. E is the error type that you have, if you don't care, just set it to any.
  3. O is the option type that you can use to configure how printing is performed. Notice that the type O is not bounded; you are free to implement it however you want!

In the example above, its a empty struct because there are no options. To see a robust and powerful example of options, see our implementation of the defaultWebLogger

Printer Type

export type Printer<S, E, O> = {
  readonly logError: boolean
  readonly logPredicate: (s: S, b: AnyAction) => boolean
  readonly printLog: (s: LogEntry<S, E>, o: O) => void

As before, S, E and O refers to state, error and options respectively.

  1. logError determines if we are logging exceptions.
  2. logPredicate determines if we should log a particular action or not.
  3. printLog is the actual place where you are free to log however you want.

LogEntry Type

export type LogEntry<S, E> = {
  readonly action: AnyAction
  readonly error: Option<E>
  readonly startedTime: Date
  readonly took: number
  readonly prevState: S
  readonly nextState: S

From above, printLog accepts 2 arguments: LogEntry<S, E> and O. This is the type signature for the former.

  1. action is the current action we are performing.
  2. error is a maybe type that may contain error if you set logError to true and an error actually occurs.
  3. startedTime is the date/time when this particular entry is logged.
  4. took is the time taken to calculate the next state.
  5. prevState is the state before redux calculations.
  6. nextState is the state after redux calculations.

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