# Inheritance

# Children

In oddlog, re-use of the same payload data is implemented via inheritance. The Logger#child method creates a new child logger that carries its own copy of the parent loggers payload. Logger#child can be called with additional payload to be merged into the payload of the new child. Similar to one-time payload passing, null would create a child without any attached payload.

const myChildLogger = logger.child(true, {additional: "payload"});

myChildLogger.info({it: "works!"}, "yay");  // payload: {additional: "payload", it: "works!"}}

myChildLogger
  .child(true, {test: 42})
  .info("pew");  // payload: {additional: "payload", test: 42}
  
myChildLogger
  .child(null)
  .info({hello: "world"}, "pew");  // payload: {hello: "world"}

# Middleware

# Express.js

For a common use-case oddlog provides some semantic sugar:

// add middleware to express.js router
router.use(logger.mwExpress());

The Logger#mwExpress method accepts arguments similar to Logger#child, but the payload argument may be a function that gets req and res passed. It will create a child logger for each incoming request and attach it to the request object as req.log. If no payload is explicitly passed, {req, res} will be used as child payload.