Let's aim to replicate what we had in Winston, at least in part, so it will be easier for you if you do full stack work, both client- and server-side. We want to have a logger object with methods such as .warn() and .info() that will display a given message in an appropriate color. Also, we don't want logs to be displayed in production. This leads us to the code as follows:

// Source file: src/logging/index.js

/* @flow */

import debug from "debug";

const WHAT_TO_LOG = "myapp:SERVICE:*"; // change this to suit your needs
const MIN_LEVEL_TO_LOG = "info"; // error, warn, info, verbose, or debug

const log = {
 error() {},
    warn() {},
    info() {},
    verbose() {},
    debug() {}
};

const logMessage = (
    color: string,
    topic: string,
    message: any = "--",
    ...rest: any
) => {
    const logger = debug(topic);
    logger.color = color;
    logger(message, ...rest);
};

if (process.env.NODE_ENV === "development") {
    localStorage.setItem("debug", WHAT_TO_LOG);

    /* eslint-disable no-fallthrough */
    switch (MIN_LEVEL_TO_LOG) {
        case "debug":
            log.debug = (topic: string, ...args: any) =>
                logMessage("gray", topic, ...args);

        case "verbose":
            log.verbose = (topic: string, ...args: any) =>
                logMessage("green", topic, ...args);

        case "info":
            log.info = (topic: string, ...args: any) =>
                logMessage("blue", topic, ...args);

        case "warn":
            log.warn = (topic: string, ...args: any) =>
                logMessage("brown", topic, ...args);

        case "error":
        default:
            log.error = (topic: string, ...args: any) =>
                logMessage("red", topic, ...args);
    }
}

export { log };

Some important details:

• The WHAT_TO_LOG constant lets you select which messages should be shown.
• The MIN_LEVEL_TO_LOG constant defines the lowest level that will be logged.
• The log object has a method for each severity level, as in Winston.
• Finally, a non-operative log object is returned if we are not in development mode; all calls to logging methods will produce exactly nothing.

We have the code we need; let's see an example of its usage.