redux-logger

What is redux-logger?

redux-logger is a middleware for Redux that logs actions and state changes to the console, making it easier to debug and understand the flow of data in your application.

What are redux-logger's main functionalities?

Basic Logging

This feature logs every action and the resulting new state to the console. It helps developers see what actions are being dispatched and how the state is changing in response.

const { createStore, applyMiddleware } = require('redux');
const logger = require('redux-logger').createLogger();
const reducer = (state = {}, action) => state;
const store = createStore(reducer, applyMiddleware(logger));
store.dispatch({ type: 'TEST_ACTION' });

Collapsed Logging

This feature collapses the log entries for each action, making the console output more compact and easier to navigate, especially when dealing with a large number of actions.

const { createStore, applyMiddleware } = require('redux');
const { createLogger } = require('redux-logger');
const logger = createLogger({ collapsed: true });
const reducer = (state = {}, action) => state;
const store = createStore(reducer, applyMiddleware(logger));
store.dispatch({ type: 'TEST_ACTION' });

Predicate Logging

This feature allows you to filter which actions get logged based on a predicate function. In this example, actions of type 'IGNORED_ACTION' will not be logged.

const { createStore, applyMiddleware } = require('redux');
const { createLogger } = require('redux-logger');
const logger = createLogger({ predicate: (getState, action) => action.type !== 'IGNORED_ACTION' });
const reducer = (state = {}, action) => state;
const store = createStore(reducer, applyMiddleware(logger));
store.dispatch({ type: 'TEST_ACTION' });
store.dispatch({ type: 'IGNORED_ACTION' });

Other packages similar to redux-logger

redux-devtools-extension

redux-devtools-extension is a package that integrates Redux with the Redux DevTools browser extension. It provides a more visual and interactive way to inspect actions and state changes, including time-travel debugging, which is not available in redux-logger.

redux-immutable-state-invariant

redux-immutable-state-invariant is a middleware that logs warnings when the state is mutated. While it doesn't log actions and state changes like redux-logger, it helps catch bugs related to state mutations, which can be a complementary tool for debugging Redux applications.

README

Logger for Redux

Install

npm i --save redux-logger

Usage

import { applyMiddleware, createStore } from 'redux';
import thunk from 'redux-thunk';
import promise from 'redux-promise';
import createLogger from 'redux-logger';

const logger = createLogger();
const createStoreWithMiddleware = applyMiddleware(thunk, promise, logger)(createStore);
const store = createStoreWithMiddleware(reducer);

Logger must be last middleware in chain, otherwise it will log thunk and promise, not actual actions (#20).

API

redux-logger exposes single constructor function for creating logger middleware.

createLogger(options?: Object)

Options

level (String)

Level of console. warn, error, info or else.

Default: log

duration (Boolean)

Print duration of each action?

Default: false

timestamp (Boolean)

Print timestamp with each action?

Default: true

colors (Object)

Object with 3 functions: prevState, action, nextState. Useful if you want paint message based on specific state or action. It also can be false if you want show plain message without colors.

• prevState(prevState: Object) => color: String
• action(action: Object) => color: String
• nextState(nextState: Object) => color: String

logger (Object)

Implementation of the console API. Useful if you are using a custom, wrapped version of console.

Default: window.console

collapsed = (getState: Function, action: Object) => Boolean

Takes a boolean or optionally a function that receives getState function for accessing current store state and action object as parameters. Returns true if the log group should be collapsed, false otherwise.

Default: false

predicate = (getState: Function, action: Object) => Boolean

If specified this function will be called before each action is processed with this middleware. Receives getState function for accessing current store state and action object as parameters. Returns true if action should be logged, false otherwise.

Default: null (always log)

stateTransformer = (state: Object) => state

Transform state before print. Eg. convert Immutable object to plain JSON.

Default: identity function

actionTransformer = (action: Function) => action

Transform action before print. Eg. convert Immutable object to plain JSON.

Default: identity function

Examples:

log only in dev mode

createLogger({
  predicate: (getState, action) => process.env.NODE_ENV === `development`
});

log everything except actions with type AUTH_REMOVE_TOKEN

createLogger({
  predicate: (getState, action) => action.type !== AUTH_REMOVE_TOKEN
});

collapse all actions

createLogger({
  collapsed: true
});

collapse actions with type FORM_CHANGE

createLogger({
  collapsed: (getState, action) => action.type === FORM_CHANGE
});

transform Immutable objects into JSON

createLogger({
  stateTransformer: (state) => {
    let newState = {};

    for (var i of Object.keys(state)) {
      if (Immutable.Iterable.isIterable(state[i])) {
        newState[i] = state[i].toJS();
      } else {
        newState[i] = state[i];
      }
    };

    return newState;
  }
});

License

MIT