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    1.1.4 • Public • Published

    Lumberjack - One Amex

    npm Travis (.org) branch

    lumberjack is a minimal and configurable Console with utilities.

    👩‍💻 Hiring 👨‍💻

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    📖 Table of Contents


    • minimal and configurable Console with utilities.
    • Log formating using formatter depending on the log level.
    • Invoke callback functions before and after writing to stream.
    • Replace global console object using lumberjack

    🤹‍ Usage


    npm i @americanexpress/lumberjack


    How to use Lumberjack

    Read more about this in the Lumberjack API section.

    import Lumberjack from '@americanexpress/lumberjack';
    function createLogger(simple = true) {
      return new Lumberjack({
        formatter: simple
          // your formatter function can be as simple as:
          ? (level, ...args) => `${level}: ${args}`
          // or can be more complex, like stringifying as JSON:
          : (level, ...messages) => JSON.stringify(
              time: (new Date()).toISOString(),
    const logger = createLogger();
    logger.error(new Error('sample error'));
    logger.warn("you're gonna have a bad time");'%d', 42);
    logger.log({ its: 'complicated' });

    How to use monkeypatches

    Read more about this in the monkeypatches API section.

    import Lumberjack, { monkeypatches } from '@americanexpress/lumberjack';
    const logger = new Lumberjack();
    console.log('This is now invoking logger.log');

    🎛️ API


    Creating a new console/Lumberjack is similar to creating a new nodejs Console, but slightly different:

    • pass a single object with named options
    const logger = new Lumberjack({
      // options are added here

    Options are:

    • stdout: stream to write to, defaults to process.stdout
    • stderr: defaults to the stdout option
    • formatter: an optional function that gets the log level and raw input arguments to return a string that is written to the stream (either stdout or stderr depending on log level)
      • defaults to util.format (nodejs Console's formatter)
      • can return null to skip writing to the stream
    • beforeWrite: callback function invoked before writing to the stream
    • afterWrite: callback function invoked after writing to the stream

    The Lumberjack instance has four methods: error, warn, info, and log.


    A monkey patch is a way for a program to extend or modify supporting system software locally (affecting only the running instance of the program).

    Use monkeypatches with care and be aware of pitfalls.


    Replaces the error, warn, info, and log methods on the global console object with those of the logger argument provided.

    import Lumberjack, { monkeypatches } from '@americanexpress/lumberjack';
    const logger = new Lumberjack();
    console.log('This is now invoking logger.log');


    Spy on invocations of methods, ex: on native packages.


    • object the method exists on
    • method name to spy on
    • spy function, receives
      • an array of the original arguments
      • a function to invoke the original method and get the return value, this will be invoked automatically if not done by the spy function

    See also attachHttpRequestSpy and attachHttpsRequestSpy

    import { monkeypatches } from '@americanexpress/lumberjack';
    monkeypatches.attachSpy(http, 'request', (args, callOriginal) => {
      console.log('starting http request', args);
      const returnValue = callOriginal(); // spy, not an interceptor, so args handled automatically
      console.log('http request started', returnValue);


    Spy on the beginning and end of an http.request.


    • spy for the invocation of http.request
    • spy for the close of the socket used in the http.request

    Both spies receive the return value of http.request and a normalized parsed URL requested (via url.parse).

    import { monkeypatches } from '@americanexpress/lumberjack';
      (clientRequest, parsedUrl) =>`started request to ${parsedUrl.href}`),
      (clientRequest, parsedUrl) =>`request to ${parsedUrl.href} finished`)


    The same thing as attachHttpRequestSpy but for the https native package.

    Note that for nodejs versions before 6.0.0 and earlier https.request called http.request so adding spys for both http and https will result in both spies being called.

    📜 Available Scripts

    npm run build

    Builds the module into the build folder.

    npm test

    Runs eslint and unit tests on the current branch.

    🏆 Contributing

    We welcome Your interest in the American Express Open Source Community on Github. Any Contributor to any Open Source Project managed by the American Express Open Source Community must accept and sign an Agreement indicating agreement to the terms below. Except for the rights granted in this Agreement to American Express and to recipients of software distributed by American Express, You reserve all right, title, and interest, if any, in and to Your Contributions. Please fill out the Agreement.

    Please feel free to open pull requests and see for commit formatting details.

    🗝️ License

    Any contributions made under this project will be governed by the Apache License 2.0.

    🗣️ Code of Conduct

    This project adheres to the American Express Community Guidelines. By participating, you are expected to honor these guidelines.


    npm i @americanexpress/lumberjack

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