Replay Functions

Replay functions are used to modify events to ensure compatibility with new applications or destinations. These functions allow for efficient reprocessing of data, ensuring your events can be smoothly integrated into new or updated systems.

How Replay Functions Work

When an event is being replayed, Replay Functions can be invoked to modify the event data. This can include changes to the event’s schema, adding, updating, or removing specific fields, or transforming the data to fit the requirements of the new application or destination.

Replay functions can be written in various languages, including JavaScript, TypeScript, Rust, and Golang. These functions are executed using WebAssembly (Wasm), ensuring maximum speed and efficiency.

Creating a Replay Function

To create a Replay function, you will need to write the function in the language of your choice and compile it to WebAssembly. Once you have compiled the function, you can upload it to Streamdal and configure it to run during the replay process.

  1. Navigate to the Streamdal console and select ‘Functions’ from the side navigation.
  2. Click on the + button to create a new function.
  3. Choose ‘Replay Function’ as the type.
  4. Write your function code in the provided editor. This code should include the logic for modifying the event data to fit the new application or destination requirements.
  5. In the test section, paste in a sample payload that your function will be working with.
  6. Build
  7. Run test and confirm no errors
  8. Deploy
  9. Associate to Replay (coming soon)

By implementing Replay Functions, you can efficiently adapt your existing events to fit new systems or updates, ensuring a smooth transition and minimizing potential integration issues.


Replay Functions are a powerful tool for managing updates and changes in your data processing systems in Streamdal. By transforming your events to fit new applications or destinations, you can ensure a smooth transition and efficient integration of your data, keeping your processes up-to-date and adaptable.