How to set a custom logger in TypeScript

Logging in Workers and Clients

The Worker comes with a default logger which defaults to log any messages with level INFO and higher to STDERR using console.error. The following log levels are listed in increasing order of severity.

Customizing the default logger

Temporal uses a DefaultLogger that implements the basic interface:

TypeScript

import { Runtime, DefaultLogger } from '@temporalio/worker';

const logger = new DefaultLogger('WARN', ({ level, message }) => {
  console.log(`Custom logger: ${level} — ${message}`);
});
Runtime.install({ logger });

JavaScript

import { Runtime, DefaultLogger } from '@temporalio/worker';

const logger = new DefaultLogger('WARN', ({ level, message }) => {
  console.log(`Custom logger: ${level} — ${message}`);
});
Runtime.install({ logger });

The previous code example sets the default logger to only log messages with level WARN and higher.

Accumulate logs for testing and reporting

TypeScript

import { DefaultLogger, LogEntry } from '@temporalio/worker';

const logs: LogEntry[] = [];
const logger = new DefaultLogger('TRACE', (entry) => logs.push(entry));
log.debug('hey', { a: 1 });
log.info('ho');
log.warn('lets', { a: 1 });
log.error('go');

JavaScript

import { DefaultLogger } from '@temporalio/worker';

const logs = [];
const logger = new DefaultLogger('TRACE', (entry) => logs.push(entry));
log.debug('hey', { a: 1 });
log.info('ho');
log.warn('lets', { a: 1 });
log.error('go');

A common logging use case is logging to a file to be picked up by a collector like the Datadog Agent.

TypeScript

import { Runtime } from '@temporalio/worker';
import winston from 'winston';

const logger = winston.createLogger({
  level: 'info',
  format: winston.format.json(),
  transports: [new transports.File({ filename: '/path/to/worker.log' })],
});
Runtime.install({ logger });

JavaScript

import { Runtime } from '@temporalio/worker';
import winston from 'winston';

const logger = winston.createLogger({
  level: 'info',
  format: winston.format.json(),
  transports: [new transports.File({ filename: '/path/to/worker.log' })],
});
Runtime.install({ logger });