When you embed a presentation on another web page, such as a blog post or personal website, the embed API lets that page communicate with it. Use it to show content related to the current slide or add your own controls for jumping to specific slides.
Messages are sent and received using JavaScript and the postMessage API. To enable this, append postMessageEvents=true to your embed URL:
https://slides.com/news/make-better-presentations/embed?postMessageEvents=true
See the reveal.js API documentation for a full list of available methods.
Example
In this working example, the parent page sends messages to and receives messages from a presentation. Open the JS tab to see the source code and comments.