[3.0.0-rc5]: Cannot colorize JSON logs

Please tell us about your environment:

• winston version?
  • winston@3
• node -v outputs: v8.10.0
• Operating System? macOS
• Language? all

What is the problem?

I am trying to write colorized JSON logs using Winston 3.x. Following the documentation, I initialized the logger like this:

module.exports = winston.createLogger({
  format: winston.format.combine(
    winston.format.colorize(),
    winston.format.json()
  ),
  transports: [new winston.transports.Console()]
})

However, when using this logger, I get encoded color codes instead of colors:

{
  "message": "An example message",
  "level": "\u001b[32minfo\u001b[39m"
}

What do you expect to happen instead?

I would have expected the log output to actually be colored.

[pdiniz13]

Something should probably be added to the docs explaining that this is the intended behavior, given that the example given in the readme is:

winston.format.combine(
  winston.format.colorize(),
  winston.format.json()
);

[indexzero]

@denisw I can see how this might be confusing, but it’s quite logical when one examines how the different formats & specifications are fighting against each other.

1. The behavior of JSON.stringify is well documented – strings must be enclosed in quotes and are escaped. Even using a custom replacer parameter I was unable to work around the string escaping for \\u chars.
2. ANSI color codes when escaped look weird – but we don’t see it because the escaping is unwrapped when written to the console – e.g. \u001b[32m instead of \\\u001b[32m.

There may be a way to get this working with a custom replacer passed to JSON.stringify, but I couldn’t get it wired up.

Instead, if we think about the desired output as what I believe it is – simply not JSON. It is JSON-like, but it’s not JSON since the strings are unescaped to allow colors to pass through. There are a lot of ways to shave the JSON-like yak, but I quickly hacked this one together to illustrate it’s possible:

const { createLogger, format, transports } = require('winston');
const util = require('util');

const logger = createLogger({
  level: 'silly',
  format: format.combine(
    format.colorize(),
    format.printf(info => {
      return Object.keys(info).reverse().reduce((acc, key, i) => {
        if (typeof key === 'string') {
          if (i > 0) acc += ", "
          acc += `"${key}": "${info[key]}"`
        }

        return acc;
      }, '{ ') + ' }';
    })
  ),
  transports: [new transports.Console()]
});

logger.info('hey colors!');
logger.error('oh and this one is red');
logger.silly('magenta maybe?');

Which when executed outputs: