types.md

Types

Logger

import { type Logger, createLogger, type pino } from '@seek/logger';

createLogger() satisfies Logger satisfies pino.Logger satisfies pino.BaseLogger;

@seek/logger includes several logger types. Its core Logger type may change between versions, which can be a hassle to coordinate if your application depends on packages that need to upgrade to the new version first.

While we try to maintain type compatibility with the pino.Logger type, it's possible that we may need to diverge in a future major version.

import { Logger, type pino } from '@seek/logger';

const logger = createLogger({
  eeeoh: {
    datadog: 'tin',
    use: 'environment',
  },
});

const warn = (logger: pino.Logger) => logger.warn('msg');

warn(logger);
//   ~~~~~~
// In a future major version, this may fail with a type error:
// Argument of type 'Logger<never>' is not assignable to parameter of type 'Logger'.

To minimise upkeep, carefully consider what logger type you are coupling your code to, and generally avoid use of the pino.Logger type.

Package code

Use structural subtyping to define a more explicit package interface. This can improve compatibility across versions of @seek/logger and with other logging implementations.

- import type { pino } from '@seek/logger';

+ type Logger = {
+   error: {
+     (msg: string): void;
+     (obj: unknown, msg: string): void;
+   };
+ };

- export const do = (logger: pino.Logger) => {
+ export const do = (logger: Logger) => {
    const error = new Error('Oops!');

    logger.warn(error, 'msg');
    logger.warn('msg');
  };

Application code

In application code that only makes use of basic logging methods, consider pino.BaseLogger:

import type { pino } from '@seek/logger';

- const basic = (logger: pino.Logger) => {
+ const basic = (logger: pino.BaseLogger) => {
  const error = new Error('Oops!');

  logger.warn(error, 'msg');
  logger.warn('msg');
};

In application code that makes use of advanced logger functionality, consider Logger:

- import type { pino } from '@seek/logger';
+ import type { Logger } from '@seek/logger';

- const advanced = (logger: pino.Logger<'asplode'>) => {
+ const advanced = (logger: Logger<'asplode'>) => {
  const childLogger = logger.child({ key: 'value' });

  childLogger.asplode('msg');
};