> For the complete documentation index, see [llms.txt](https://stampit.js.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://stampit.js.org/api/properties.md).

# Properties

You can add properties to the objects created from your stamps. These are default properties of your objects.

```javascript
const HasLog = stampit({
  props: {
    log: require('bunyan').createLogger({ name: 'my logger' })
  }
})

const loggerObject = HasLog()
loggerObject.log.debug('I can log')
```

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

```javascript
const RequestHandler = stampit(HasLog) // composing with HasLog
.methods({
  handle(req, res, next) {
    this.log.info({ originalUrl: req.originalUrl }, 'handling request') // using the .log
    res.sendStatus(200)
  }
})

const handler = RequestHandler()
handler.log.debug('Created a handler')
```

## Descriptor merging algorithm

The properties are copied **by assignment**. In other words - **by reference** using `Object.assign`.

```javascript
HasLog().log === RequestHandler().log
```

In case of conflicts the last composed property wins.

## Other ways to add properties

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

```javascript
const myLogger = require('bunyan').createLogger({ name: 'my logger' })

const HasLog = stampit({
  props: {
    log: myLogger
  }
})

const HasLog = stampit({
  properties: {
    log: myLogger
  }
})

const HasLog = stampit.props({
  log: myLogger
})

const HasLog = stampit.properties({
  log: myLogger
})

const HasLog = stampit().props({
  log: myLogger
})

const HasLog = stampit().properties({
  log: myLogger
})
```


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://stampit.js.org/api/properties.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.