MIGRATE-v3.md

How to migrate from v2 to v3

If importing from eventsource-parser

The parser now takes an object of callbacks instead of only an onParse callback. This means you do not have to check the type of the event in the onEvent callback, but instead provide separate callbacks for each event type:

-import {createParser, type ParsedEvent, type ReconnectInterval} from 'eventsource-parser'
+import {createParser, type EventSourceMessage} from 'eventsource-parser'

-const parser = createParser((event: ParsedEvent | ReconnectInterval) => {
-  if (event.type === 'event') {
-    // …handle event…
-  } else if (event.type === 'reconnect-interval') {
-    // …handle retry interval change…
-  }
-})
+const parser = createParser({
+  onEvent: (event: EventSourceMessage) => {
+    // …handle event…
+  },
+  onRetry: (interval: number) => {
+    // …handle retry interval change…
+  }
+})

The parser also now has a onError callback that you can use to handle parse errors, as well as an onComment callback that you can use to handle comments:

const parser = createParser({
  onEvent: (event: EventSourceMessage) => {
    // …handle event…
  },
  onRetry: (interval: number) => {
    // …handle retry interval change…
  },
  onError: (error: Error) => {
    // …handle parse error…
  },
  onComment: (comment: string) => {
    // …handle comment…
  },
})

Renamed types:

• ParsedEvent => EventSourceMessage (and type property is removed)

Removed types:

• EventSourceParseCallback - replaced with ParserCallbacks interface (onEvent property)
• ReconnectInterval - no longer needed, as the onRetry callback now provides the interval directly
• ParseEvent - no longer needed - the different event types are now handled by separate callbacks

If using the TransformStream variant

No change is neccessary, but you can now subscribe to changes in the retry interval by providing a callback to the onRetry option when creating the stream:

const stream = new EventSourceParserStream({
  onRetry: (interval: number) => {
    // …handle retry interval change…
  },
})

There is also a new option to specify how parse should be handled - by default it will ignore them, but you can choose to terminate the stream or handle it manually:

const stream = new EventSourceParserStream({
  onError: (error: Error) => {
    // …handle parse error…
  },
})

// …or…
const stream = new EventSourceParserStream({
  onError: 'terminate',
})

Lastly, if you're interested in any comments that are encountered during parsing, you can provide a callback to the onComment option:

const stream = new EventSourceParserStream({
  onComment: (comment: string) => {
    // …handle comment…
  },
})