Outputs

Outputs determine where and how log records are written.

Built-in Outputs

(You don't need to pass these in if you're happy with the default behavior. Note that the format convenience setting on the Logger will override/replace the outputs array if used.)

import { ConsolePrettyOutput, ConsoleJsonOutput } from '@versionzero/logger';

// if a terminal, use pretty formatting.  otherwise default to data logging. 
let consoleOutput = tty.isatty(1)? new ConsolePrettyOutput() : new ConsoleJsonOutput();

// Create logger with selected output
const logger = new Logger({outputs: [consoleOutput]});

Custom Outputs

Create custom outputs by implementing the output(record) method:

class SlowSlowMessageOutput {
  constructor() {
    this.queue = [];
    this.processing = false;
  }
  // synchronous call!  (anything complex should be queued for asynchronous processing)
  output(record) {
    // this example output filters records based on the value of a field...
    if (record.dt > 10000) {
      this.queue.push(record);
      void this.processQueue();  // fire and forget
    }
  }
  async processQueue() {
    if (this.processing) { return }
    this.processing = true;
    while (this.queue.length > 0) {
      await setTimeout(1000);
      const record = this.queue.shift();
      console.log('slowly logged slow transaction:', record.msg);
    }
    this.processing = false;
  }
}

const slowLogger = new Logger({ outputs: [new SlowSlowMessageOutput()] });

for (let i = 0; i < 100; i++) {
  let dt = Math.random() * 11000;
  slowLogger.info({i, dt}, `transaction ${i} took ${dt}ms`);
}
logger.notice('slow logs are now being processed asynchronously');