react-native-logs

Performance-aware simple logger for React-Native with custom levels and transports (colored console, file writing, etc.). Each level has its severity: a number that represents its importance in ascending order from the least important to the most important. Eg. debug:0, info:1, warn:2, error:3. By config the logger with a minium severity level, you will see only the logs that have it highest. Then logs will be managed by transport: the function that will display/save/send log messages. It is also possible to create namespaced logs that allow logging to be enabled only for certain parts of the app.

Why another logging library?

After trying the most known logging libraries, like winston and bunyan, we found that for react-native we needed something simpler, but still flexible, and without dependencies on nodejs (we don't like the rn-nodeify solution). Comments and suggestions are welcome.

Installation

npm install --save react-native-logs

OR

yarn add react-native-logs

Quick Start

import { logger } from "react-native-logs";

var log = logger.createLogger();

log.debug("This is a Debug log");
log.info("This is an Info log");
log.warn("This is a Warning log");
log.error("This is an Error log");

By default the createLogger() method (called without arguments) will create a simple console logger with debug, info, warn and error levels.

Configuration

You can customize the logger by passing a config object to the createLogger method (see example below). All params are optional and will take default values if no corresponding argument is passed.

Example with common configuration:

import { logger, consoleTransport } from "react-native-logs";

const defaultConfig = {
  severity: "debug",
  transport: consoleTransport,
  transportOptions: {
    color: "ansi", // custom option that color consoleTransport logs
  },
  levels: {
    debug: 0,
    info: 1,
    warn: 2,
    error: 3,
  },
  async: true,
  dateFormat: "time",
  printLevel: true,
  printDate: true,
  enabled: true,
};

var log = logger.createLogger(defaultConfig);

Parameter	Type	Description	Default
severity	string	Init logs severity (least important level you want to see)	debug (or the first custom level)
transport	Function	The transport function for logs (see below for presets)	The preset transport consoleTransport
transportOptions	Object	Set custom options for transports	null
levels	Object	Set custom log levels: {name:power}	false
async	boolean	Set to true for async logs (to improve app performance)	true
asyncFunc	Function	Set a cutom async function (cb: Function)=>{return cb()}	InteractionManager.runAfterInteractions
dateFormat	string	Choose between only time or a date: local, utc, iso	time
printLevel	boolean	Choose whether to print the log level	true
printDate	boolean	Choose whether to print the log date/time	true
enabled	boolean	Enable or disable logging	true
enabledExtensions	string[]	List of enabled namepaces	[]

Custom levels

Log levels have this format: { name : severity } and you can create your personalized list, Eg:

import { logger } from "react-native-logs";

const config = {
  levels: {
    trace: 0,
    info: 1,
    silly: 2,
    error: 3,
    mad: 4,
  },
};

var log = logger.createLogger(config);

Custom transport

You can write your own transport to send logs to a cloud service, save it in to a database, or do whatever you want. The following parameters are received by the function:

• msg: any: the message formatted by logger "[time] | [namespace] | [level] | [msg]"
• rawMsg: any: the message (or array of messages) in its original form
• level: { severity: number; text: string }: the log level
• extension?: string | null: its namespace if it is an extended log
• options?: any: the transportOptions object

You can define your custom transport as follow (example in typescript):

import { logger, transportFunctionType } from "react-native-logs";

const customTransport: transportFunctionType = (props) => {
  // Do here whatever you want with the log message
  // You can use any options setted in config.transportOptions
  // Eg. a console log: console.log(props.level.text, props.msg)
};

const config = {
  transport: customTransport,
};

var log = logger.createLogger(config);

Transport Options

By setting the transportOptions parameter you can insert the options that will be passed to transports. For some transports these may be mandatory, as in the case of the FS option for the fileAsyncTransport (see preset transports list for details).

import { logger, fileAsyncTransport } from "react-native-logs";
import RNFS from "react-native-fs";

const config = {
  transport: fileAsyncTransport,
  transportOptions: {
    FS: RNFS,
    fileName: `log.txt`,
  },
};

var log = logger.createLogger(config);

Multiple Arguments

Log messages can be concatenated by adding arguments to the log function:

var errorObject = {
  staus: 404,
  message: "Undefined Error",
};
log.error("New error occured", errorObject);

Preset transports

react-native-logs includes some preset transports. You can import the one of your choice: import { logger, <transportName> } from 'react-native-logs';

Example:

import { logger, consoleTransport } from "react-native-logs";

const config = {
  transport: consoleTransport,
  transportOptions: {
    colors: `ansi`,
  },
};

var log = logger.createLogger(config);

List of included preset transports

consoleTransport

Print the logs with a formatted console.log output.

name	type	description	default
colors	string	Choose between null (no colors), web (colors for chrome console), ansi (colors for system or vscode console)	null

fileAsyncTransport

This transport requires the installation of react-native-fs(install tutorial here) or expo-file-system(beta), and allows you to save the logs on the <filePath>/<fileName>.txt file.

Accepted Options:

name	type	description	default
FS	Object	MANDATORY, filesystem instance for the transport (RNFS or expo FileSystem)	null
fileName	string	set logs file name	log
filePath	string	set logs file path	RNFS.DocumentDirectoryPath or expo FileSystem.documentDirectory

Example:

import { logger, fileAsyncTransport } from "react-native-logs";
import RNFS from "react-native-fs";
/* EXPO:
 * import * as FileSystem from 'expo-file-system';
 */

let today = new Date();
let date = today.getDate();
let month = today.getMonth() + 1;
let year = today.getFullYear();

const config = {
  severity: "debug",
  transport: fileAsyncTransport,
  transportOptions: {
    FS: RNFS,
    /* EXPO:
     * FS: FileSystem,
     */
    fileName: `logs_${date}-${month}-${year}`, // Create a new file every day
  },
};

var log = logger.createLogger(config);

log.info("Print this string to a file");

NOTE: Following this example it will be possible to upload the file to your remote server

sentryTransport

Send logs to Sentry. This transport also tries to send the error stack if it receives a JS error.

Accepted Options:

name	type	description	default
SENTRY	Object	MANDATORY, sentry instance for the transport	null

Example:

import { logger, sentryTransport } from "react-native-logs";
import * as Sentry from "@sentry/react-native";

/*
 * Configure sentry
 */

const config = {
  severity: "debug",
  transport: sentryTransport,
  transportOptions: {
    SENTRY: Sentry,
  },
};

var log = logger.createLogger(config);

log.error("Send this log to Sentry");

Extensions (Namespaced loggers)

To enable logging only for certain parts of the app, you can extend the logger to different namespaces using the "extend" method. You can enable these extensions from the configuration (config.enabledExtensions) or by using the enable/disable methods.

Example:

import { logger, consoleTransport } from "react-native-logs";

const config = {
  transport: consoleTransport,
  transportOptions: {
    colors: `ansi`,
  },
  enabledExtensions: ['ROOT','HOME']
};

var log = logger.createLogger(config);
var rootLog = log.extend('ROOT');
var homeLog = log.extend('HOME');
var profileLog = log.extend('PROFILE');

log.debug('print this'): // this will print "<time> | DEBUG | print this"
rootLog.debug('print this'): // this will print "<time> | ROOT | DEBUG | print this"
homeLog.debug('print this'): // this will print "<time> | HOME | DEBUG | print this"
profileLog.debug('not print this'): // this extension is not enabled

Methods

enable/disable

Dynamically enable/disable loggers and extensions, if it is called without parameters then it will disable/enable the whole logger:

import { logger } from "react-native-logs";

var log = logger.createLogger();
var rootLog = log.extend('ROOT');

rootLog.info('not print this'): // this extension is not enabled
log.enable('ROOT');
rootLog.info('print this'): // this will print "<time> | ROOT | INFO | print this"
log.disable('ROOT');
rootLog.info('not print this'): // this extension is not enabled

getExtensions

Get an array of currently created extensions.

setSeverity

You can set the severity level by passing the name(string) of the least important level you want to see. This method will overwrite any config.severity option set in logger creation.

var log = logger.createLogger();

log.setSeverity("info");
log.debug("This log will not be printed");
log.info("This log will be printed correctly");
log.error("This log will be printed correctly");

getSeverity

You can get the current severity level setted.

var log = logger.createLogger();

var defaultseverity = log.getSeverity(); // severity = debug
log.setSeverity("info");
var severity = log.getSeverity(); // severity = info
log.setSeverity("error");
var newseverity = log.getSeverity(); // newseverity = error

Usage Tips

Logs only in development mode

In reacly-native, after you have create your logger, you can set to log only in development using the __DEV__ as follows:

import { logger, consoleTransport, fileAsyncTransport } from "react-native-logs";
import RNFS from "react-native-fs";

const config = {
  transport: __DEV__ ? consoleTransport : fileAsyncTransport,
  severity: __DEV__ ? "debug" : "error",
  transportOptions: {
    colors: `ansi`,
    FS: RNFS,
  },
};

var log = logger.createLogger();

This will block all the logs in production, but not the errors, so the app performance will not be affected. This will also change the transport: print to console in development and save to file in production.

Global logger in react-native

In order to have a global logger throughout the app, i recommend using a config.js file to initialize the logger so it can be imported wherever it is needed. Example:

//config.js
import { logger, consoleTransport, fileAsyncTransport } from "react-native-logs";
import RNFS from "react-native-fs";

const config = {
  transport: __DEV__ ? consoleTransport : fileAsyncTransport,
  severity: __DEV__ ? "debug" : "error",
  transportOptions: {
    colors: `ansi`,
    FS: RNFS,
  },
};

var LOG = logger.createLogger(config);

export { LOG };

//index.js and other app files
import { LOG } from "./config";

LOG.info("app log test");

To use extended loggers in all files you can also re-declare them:

//root.js
import { LOG } from "./config";
var log = LOG.extend("ROOT");

log.info("root log test");

//root2.js
import { LOG } from "./config";
var log = LOG.extend("ROOT");

log.info("root log test");

//home.js
import { LOG } from "./config";
var log = LOG.extend("HOME");

log.info("home log test");

Use multiple transports

To use multiple transports for logs, just create a transport function that calls other transport functions as follows:

import {
  logger,
  consoleTransport,
  fileAsyncTransport,
  sentryTransport,
  transportFunctionType,
} from "react-native-logs";
import RNFS from "react-native-fs";
import * as Sentry from "@sentry/react-native";

var customTransport: transportFunctionType = (props) => {
  // Do here whatever you want with the log message
  // Eg. a console log: console.log(props.level.text, props.msg)
};

const log = logger.createLogger({
  transport: (props) => {
    consoleTransport(props);
    fileAsyncTransport(props);
    sentryTransport(props);
    customTransport(props);
  },
  transportOptions: {
    FS: RNFS,
    SENTRY: Sentry,
    colors: "ansi",
  },
});