Function to print multiple arguments together for logging

Question

I am trying to write a generic log function that will accept string and object type of arguments of variable length and print them with some metadata related to the modules and sub modules. But I can't figure out a way print all the arguments together. Currently I am doing this.

// MODULE_NAME is different for every module of my project, so
// that I know which module the log belongs to.

function myLogger() {
  for (var i = 0; i < arguments.length; i++) {
    console.log(MODULE_NAME, ":", arguments[i]);
  }
}

I am looking for a better way to do it which will work for following examples.

// MODULE_NAME = "TEST"
myLogger("error");
myLogger("error", err, ", result", res);
myLogger("hello", "world");

Output of the above calls should be

TEST : error
TEST : error {obj}, result {obj} 
TEST : hello world

You could use join to join them.

Andrew Li
– Andrew Li

2017-08-08 07:26:02 +00:00
Commented Aug 8, 2017 at 7:26 — Andrew Li
– Andrew Li, Commented Aug 8, 2017 at 7:26

Madara's Ghost · Accepted Answer · 2017-08-08 07:27:48Z

2

console.log actually accepts variadic arguments. You can do something like

function myLogger(...args) {
  console.log(MY_MODULE, ...args);
}

to pass all the arguments directly into console.log.

If your ~~life~~ company sucks and you can't use modern JS (with a transpiler), you can use .apply()

function myLogger() {
  console.log.apply(console, [MY_MODULE].concat(arguments));
}

answered Aug 8, 2017 at 7:27

Madara's Ghost

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1 Comment

molecule Over a year ago

This works for me I. I am using latest version for JS :D . Thanks mate !

Mrugesh · Accepted Answer · 2017-08-08 07:34:18Z

You can use winston logger.Through which you can generate five different level of logs. Please see my code below:

const winston = require('winston');
const fs = require('fs');
const env = process.env.NODE_ENV || 'development';
const logDir = 'log';
// Create the log directory if it does not exist
if (!fs.existsSync(logDir)) {
    fs.mkdirSync(logDir);
}
const tsFormat = () => (new Date()).toLocaleTimeString();
const logger = new(winston.Logger)({
    transports: [
        // colorize the output to the console
        new(winston.transports.Console)({
            timestamp: tsFormat,
            colorize: true,
            level: 'info'
        }),
        new(require('winston-daily-rotate-file'))({
            filename: `${logDir}/-results.log`,
            timestamp: tsFormat,
            datePattern: 'yyyy-MM-dd',
            prepend: true,
            level: env === 'development' ? 'verbose' : 'info'
        })
    ]
});
 logger.debug('Debugging info');
 logger.verbose('Verbose info');
 logger.info('Hello world');
 logger.warn('Warning message');
 logger.error('Error info');

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