travetto: Log

This module provides logging functionality relying up the built in console operations. This is achieved via AST transformations. The code is rewritten at compile time to transform the console operations into proper logging commands. In addition to the transformation, class name and line number are added to the log messages to provide additional context.

The supported operations are:

• console.fatal which logs at the FATAL level
• console.error which logs at the ERROR level
• console.warn which logs at the WARN level
• console.info which logs at the INFO level
• console.debug which logs at the DEBUG level
• console.trace which logs at the TRACE level
• console.log which logs at the INFO level

Note: In production mode, all console.debug and console.trace invocations are compiled away for performance/security reasons. This means that the code is actually removed, and will not execute.

A sample of the transformation would be:

function work() {
  console.trace('Start Work');
  ...
  try {
    ... bad invocation ...
  } catch (e) {
    console.error(e);
  }
  console.trace('End Work');
}

Which, when in dev mode transforms into:

function work() {
  Logger.log('trace', 'Start Work');
  try {
    ... bad invocation ...
  } catch (e) { 
    Logger.log('error', e);
  }
  Logger.log('trace', 'End Work');
}

And when in prod mode transforms into:

function work() {
  try {
    ... bad invocation ...
  } catch (e) { 
    Logger.log('error', e);
  }
}

The logging output, as indicated provides context for location of invocation. Given the file test/simple.ts:

console.log('Hello World');

console.log('Woah!', { a: { b: { c: { d: 10 } } } });

console.info('Woah!');

console.debug('Test');

console.fatal('hi');

The corresponding output would be

2018-06-23T16:57:58 info  [test.simple:  5] Hello World
2018-06-23T16:57:58 info  [test.simple:  7] Woah! { a: { b: { c: [Object] } } }
2018-06-23T16:57:58 info  [test.simple:  9] Woah!
2018-06-23T16:57:58 debug [test.simple: 11] Test
2018-06-23T16:57:58 fatal [test.simple: 13] hi