How do I bind a bunyan logging function to a class function in ES6?

Question

Fussing with this one a bit today, still getting an error. Docs here. Closest I have is this:

constructor(region, sslEnabled = true, 
     logger = () => {}, errorLogger = () => {}) {
if (region === undefined || !region)
  throw new Error("Initialization error: region is required");

  this.log = () => {};           // these two lines might be unnecessary
  this.logError = () => {};      //
  this.log = logger.bind(this);
  this.logError = errorLogger.bind(this);
  this.region = region;
  this.sslEnabled = sslEnabled;
}

Elsewhere in the class I send a bunyan logger's functions in:

const tools = new Tools(
  config.region,
  config.ssl,
  logger.debug,
  logger.error
);

The logger is just using console output. This works if I pass console.log and console.error but fails if I pass Bunyan loggers:

bunyan usage error: /usr/src/app/src/healthcheck.js:47: 
 attempt to log with an unbound log method: `this` is: TTools {
  log: [Function: bound ],
  logError: [Function: bound ],
  region: 'us-west-2',
  sslEnabled: false }

There is a github issue about this but it didn't really make it clear how to fix it. How do I pass a bunyan logger function like logger.error to another object? Is this possible?

Answer 1

If its complaining about this then that's because the this context is lost when you send logger.debug function.

Use ES6 fat arrow function to get around this problem.

const tools = new Tools(
  config.region,
  config.ssl,
  x => logger.debug(x),
  x => logger.error(x)
);