Winston: The function 'log' is not bound with logger instance, resulting error when calling function 'log' without the logger instance

[darrenqc]

My problem is, if I'm gonna use function 'log' alone, like passing function 'log' to some other object, am I suppose to write object.log = logger.log.bind(logger) instead of object.log = logger.log, or should winston take care of the binding?

const winston = require('winston');

/* Either way of declaring logger instance is not working
let logger = winston.loggers.get('some_name');
logger.configure({
    level: 'info',
    transports: [
        new (winston.transports.File)({filename: './some_log_file.log'})
    ]
});
*/

let logger = new (winston.Logger)({
    level: 'info',
    transports: [
        new (winston.transports.File)({filename: './some_log_file.log'})
    ]
})

let log = logger.log;

log('info', 'hello world');

Running the code above will result in the following error

/home/darren/projects/sp/node_modules/winston/lib/winston/logger.js:140
  if (this._names.length === 0) {
                 ^

TypeError: Cannot read property 'length' of undefined
    at Logger.log (/home/darren/projects/sp/node_modules/winston/lib/winston/logger.js:140:18)
    at Object.<anonymous> (/home/darren/projects/sp/testwinston.js:23:1)
    at Module._compile (module.js:541:32)
    at Object.Module._extensions..js (module.js:550:10)
    at Module.load (module.js:458:32)
    at tryModuleLoad (module.js:417:12)
    at Function.Module._load (module.js:409:3)
    at Module.runMain (module.js:575:10)
    at run (bootstrap_node.js:352:7)
    at startup (bootstrap_node.js:144:9)

However, if we use the default logger, everything works just fine.

// outputs "info: hello world" to the console
const winston = require('winston');

let log = winston.log;

log('info', 'hello world');

[darrenqc]

@chilts @indexzero @FotoVerite @nanek @npeeples Sorry for my being rude guys, but I really need your help.

[WarShoe]

I use meteor-react framework, and even the default logger example does not work for me. The error is more-or-less the same:

Uncaught TypeError: Cannot read property 'write' of undefined

It looks that this software has rotten.

[nanek]

With a custom logger:

let log = logger.log;

log('info', 'hello world');

will error as the issue description states, the callee is changing. That is this is different. If you execute from the logger object, it works as expected:

logger.log('info', 'hello world');

I can confirm this is how the library currently behaves. I'm not able to comment on whether this is by design or something the library wants to fix.

@WarShoe Your issue might be different. Please confirm you are passing the logger object, not the log function around when using a custom logger. If the issue persists, I recommend creating a new issue.

[jcrugzz]

Why not pass around the logger and use logger.info('message') logger.error('My error message')? This is just how javascript works. You plucked a function without preserving its context. If you want to pass around the log function rather than the logger you should bind it yourself. I just think it makes more sense to pass around the logger as thats the point

[darrenqc]

@nanek @jcrugzz Thank you. I should be passing around the logger.

[Celadora]

We found a quick fix for this. Simply bind the logger to the log function:
var boundLogger = logger.log.bind(logger);

Then just use the boundLogger in place of logger.log.

The reason for doing it this way is to remain logger agnostic - not all loggers will have methods: info, error, and so-forth. Using just one method, log, keeps it simple.

[leviwheatcroft]

If this is by design that's fine, but the package should throw a descriptive error.

@jcrugzz has a point in that, "that's how javascript works", however in this particular case I think lots of consumers will give it a try because logger.log seems so redundant.

As in, a common pattern is to have a module to instantiate and configure a winston instance, and looking at the readme it's reasonable to conclude that once your logger is configured you don't need to expose it to the rest of your app.