/console-log-json

A universal JSON logger that plugs in to the existing `console.log` native function. console.log() anything and have the output be formatted to single line JSON, including stack traces, so that it can be easily parsed by tool such as LogDNA or other log ingestion service that reads JSON.

Primary LanguageTypeScriptMIT LicenseMIT

console-log-json

title

A universal JSON logger that plugs in to the existing console.log native function.

Pupose and Description

A no fuss simple drop-in replacement for console.log(), console.info(), console.error() to handle anything you throw at it and have the output be formatted to a consistent format in a single JSON line of text, including stack traces (if passing an error object), so that it can be easily parsed by tool such as LogDNA.

Features

  • The order of parameters or number of parameters don't matter, it figures out how to log it.
  • Handles circular references
  • Automatically add a date stamp in UTC to every log.
  • Automatically parse stack traces and format them into a single line for for easy parsing in log management software such as LogDNA.
  • Log extra context if passed in.
  • Won't crash out and cause the application to stop, if there is a problem with logger, instead try to fall back to original console.log, output what is possible and continue.
  • Logging is done in a non awaiting promise so that we yield to other processing while logging
  • Logs via error level when message contains the word "error" to properly flag errors even if a mistake is made using the wrong console.info instead of console.error.

Usage

  1. Install 
    npm install console-log-json
  2. At the entry point of the application include the package and run LoggerAdaptToConsole() 
    import { LoggerAdaptToConsole } from "console-log-json";
LoggerAdaptToConsole();
    This will adapt console.log(), console.error(), etc... to take in any string, or object, in any order or any number of them, and it will log a consistently formatted single line JSON to console. For example: 
    console.warn('this is a message', {'some-extra-data': 'hello'});
    will produce: 
    {"level":"warn","message":"this is a message","some-extra-data":"hello","@timestamp":"2019-11-29T21:44:40.463Z"}

Environment Variable Options

To suppress some bits of the log to make it less noisy you can set these environment variables:

  • CONSOLE_LOG_JSON_NO_FILE_NAME="true"
    • Omits @filename in log
  • CONSOLE_LOG_JSON_NO_PACKAGE_NAME="true"
    • Omits @packageName in log
  • CONSOLE_LOG_JSON_NO_TIME_STAMP="true"
    • Omits @timestamp in log
  • CONSOLE_LOG_JSON_NO_STACK_FOR_NON_ERROR="true"
    • Omits @logCallStack in log
  • CONSOLE_LOG_JSON_NO_LOGGER_DEBUG="true"
    • Omits _loggerDebug in log
  • CONSOLE_LOG_JSON_NO_NEW_LINE_CHARACTERS="true"
    • Omits \n new line characters in the log string. -- the presence of these can help format the log for readability for some log analyzers. But it can cause problems for others. You can turn them off with this.

Examples

1. Logging an error object

const err = new Error('this is a test');
console.log('hello world', err);

Will produce:

{"level":"error","message":"hello world - this is a test","stack":"Error: this is a test    at Context.<anonymous> (console-log-json/test/logger.test.ts:260:17)    at callFn (console-log-json/node_modules/mocha/lib/runnable.js:387:21)    at Test.Runnable.run (console-log-json/node_modules/mocha/lib/runnable.js:379:7)    at Runner.runTest (console-log-json/node_modules/mocha/lib/runner.js:535:10)    at console-log-json/node_modules/mocha/lib/runner.js:653:12    at next (console-log-json/node_modules/mocha/lib/runner.js:447:14)    at console-log-json/node_modules/mocha/lib/runner.js:457:7    at next (console-log-json/node_modules/mocha/lib/runner.js:362:14)    at Immediate._onImmediate (console-log-json/node_modules/mocha/lib/runner.js:425:5)    at processImmediate (internal/timers.js:439:21)","@timestamp":"2019-11-29T21:55:33.443Z"}
  • Notice the log level error is automatically chosen even though we used console.log() instead of console.error() this is because we passed in a error object, so it makes sense to log it as log level error.
  • Notice the stack trace is included and formatted into one line as to not interfere with logging services such as LogDNA. This allows them to interpret the whole thing as a single log event, rather than spread out over multiple lines, possibly even interweaved with other logs.
  • The string "hello world" is included together with the same log.
  • Any number of additional strings or objects can be included in the console.log() parameters, in any order and it will be handled consistently and sensibly.

2. Including extra information as an object

const extraInfo = {firstName: 'homer', lastName: 'simpson'};
console.log(extraInfo, 'hello world');

Will produce:

{"level":"info","message":"hello world","age":25,"firstName":"homer","lastName":"simpson","location":"mars","@timestamp":"2019-12-01T04:10:38.861Z"}
  • Notice that even though we supplied hello world as the last parameter it is still logged out as the message property and is always the first thing after the log level
  • Notice the extraInnfo data is split out and included as individual properties at the top level ready for easy parsing and filtering in logging tools such as LogDNA.

3. You may include multiple objects, it will deal with them all

const extraInfo1 = {firstName: 'homer', lastName: 'simpson'};
const extraInfo2 = {age: 25, location: 'mars'};
console.log(extraInfo1, 'hello world', extraInfo2);

Will produce:

{"level":"info","message":"hello world","age":25,"firstName":"homer","lastName":"simpson","location":"mars","@timestamp":"2019-12-01T04:10:38.861Z"}
  • Again notice that we are not picky about the order in which the parameters are passed in to console.log()
  • Notice that properties fo extraInfo1 and extraInfo2 are extracted and all logged in on line at the top level for easy parsing and filtering in logging tools such as LogDNA.
  • Notice that properties such as firstName and age etc are sorted alphabetically for consistent appearance of logs in JSON no matter what order they are passed in.