You can add methods (aka functions) to the objects created from your stamps.

const Logger = stampit({
  methods: {
    debug(str) {
      console.log(str)
    }
  }
})
​
const logger = Logger()
​
logger.debug('Server started')

All the methods are attached to object's prototype.

logger.__proto__.debug === Logger.compose.methods.debug

Moreover, the entire methods descriptor metadata becomes the prototype.

logger.__proto__ === Logger.compose.methods

If you compose the stamp above with any other stamp, then object instances created from it will also have the .debug method.

const Server = Logger.compose({
  methods: {
    async start() {
      this.debug('Server started')
    }
  }
})
​
const server = Server()
​
server.debug('Starting server')
server.start()

Descriptor merging algorithm

The methods are copied by assignment. In other words - by reference using Object.assign.

Logger().debug === Server().debug

In case of conflicts the last composed method wins. To avoid method collision use the @stamp/collision stamp. To make sure a method is implemented use the @stamp/required stamp.

NOTE

When using the @stamp/required stamp it creates a proxy object and returns from the factory. This means that logger.__proto__ === Logger.compose.methods or logger.__proto__.debug === Logger.compose.methods.debug will no longer be true.

Other ways to add methods

Exactly the same stamp can be created in few ways. Here they all are.

function myDebug(str) {
  console.log(str)
}
​
const Logger = stampit({
  methods: {
    debug: myDebug
  }
})
​
const Logger = stampit.methods({
  debug: myDebug
})
​
const Logger = stampit().methods({
  debug: myDebug
})