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Substreams Sink Examples - JS

The Substreams JS library allows you to consume Substreams packages using the JavaScript programming language. The library works on both NodeJS and the Browser, but with some differences.

Persisting the Cursor

Consuming a Substreams package involves opening a stream long-live gRPC connection. Disconnections will happen and it is necessary to create a reconnection mechanism that starts reading exactly where the stream was interrupted. The cursor provided by Substream must be persisted and, in the case of a disconnection, the latest committed cursor must be used.

You can read more about this topic in the Substreams docs.

NodeJS vs Browser

  • Libraries: running Substreams JS on NodeJS requires using the @connectrpc/connect-node library, while consuming packages on the browser requires using @connectrpc/connect-web.
  • Persisting the cursor: when using NodeJS, you can persist the cursor in a file or a database. When using the browser, you can use the local storage, cookies or an external API.