extend.md

Extending electron-log

Each process in Electron has its own electron-log instance, so make sure you define a custom transport or hook in each process. It's a good idea to save such a code in a separated file and require it from inside each process.

Transport

Transport is just a function (msg: LogMessage) => void, so you can easily override/add your own transport.

import util from 'util';

log.transports.console = (message) => {
  const text = util.format.apply(util, message.data);
  console.log(`[${message.date.toLocaleTimeString()} ${message.level}] ${text}`);
};

Please be aware, if you override a transport function the default transport options (like level or format) will be undefined.

transforms

Each transport has a transform option which is an array of functions. Before doing some work, a log message is passed through each transform function to format data before processing.

A transform has the following interface:

({ data, message, logger, transport }) => any;

It returns a message data property with some transformations applied.

Example of adding a custom transform function

log.transports.file.transforms.push(({ data }) => {
  if (data.includes('paynment')) {
    return ['[PAYNMENT]', ...data];
  }
  
  return data;
});

Hooks

In some situations, you may want to get more control over logging. Hook is a function which is called on each transport call.

(msg: LogMessage, transport: Transport) => LogMessage

Hook function return original or modified message. If the hook function returns false, the current transport will be skipped.

In this example the file transport is disabled for all messages which contain 'password' phrase:

log.hooks.push((message, transport) => {
  if (transport !== log.transports.file) {
    return message;
  }

  if (message.data[0].includes('password')) {
    return false;
  }

  return message;
});

Log levels

Add a new "notice" level before "info" (index = 2):

log.addLevel('notice', 2);
log.notice('New level added');

Also, you can add TypeScript type definition:

electron-log.extend.d.ts:

import 'electron-log'

declare module 'electron-log' {
  interface LogFunctions {
    notice(...params: any[]): void;
  }
}

LogMessage

• data: any[] Arguments passed to log function
• date: Date
• level: 'error' | 'warn' | 'info' | 'verbose' | 'debug' | 'silly'
• logId: string
• scope: string | undefined
• variables?: { [name: string]: any } When log message is created, values from log.variables are saved here (to make it possible to pass message between different processes)

See more details in the type definition