# eventsource-parser

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A streaming parser for [server-sent events/eventsource](https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events), without any assumptions about how the actual stream of data is retrieved. It is intended to be a building block for clients and polyfills in javascript environments such as browsers, node.js and deno.

You create an instance of the parser, and _feed_ it chunks of data - partial or complete, and the parse emits parsed messages once it receives a complete message. A [TransformStream variant](#stream-usage) is also available for environments that support it (modern browsers, Node 18 and higher).

## Installation

```bash
npm install --save eventsource-parser
```

## Usage

```ts
import {createParser, type ParsedEvent, type ReconnectInterval} from 'eventsource-parser'

function onParse(event: ParsedEvent | ReconnectInterval) {
  if (event.type === 'event') {
    console.log('Received event!')
    console.log('id: %s', event.id || '<none>')
    console.log('name: %s', event.name || '<none>')
    console.log('data: %s', event.data)
  } else if (event.type === 'reconnect-interval') {
    console.log('We should set reconnect interval to %d milliseconds', event.value)
  }
}

const parser = createParser(onParse)
const sseStream = getSomeReadableStream()

for await (const chunk of sseStream) {
  parser.feed(chunk)
}

// If you want to re-use the parser for a new stream of events, make sure to reset it!
parser.reset()
console.log('Done!')
```

## Stream usage

```ts
import {EventSourceParserStream} from 'eventsource-parser/stream'

const eventStream = response.body
  .pipeThrough(new TextDecoderStream())
  .pipeThrough(new EventSourceParserStream())
```

Note that the TransformStream is exposed under a separate export (`eventsource-parser/stream`), in order to maximize compatibility with environments that do not have the `TransformStream` constructor available.

## License

MIT © [Espen Hovlandsdal](https://espen.codes/)