eventsource
WhatWG/W3C-compatible server-sent events/eventsource client. The module attempts to implement an absolute minimal amount of features/changes beyond the specification.
If you're looking for a modern alternative with a less constrained API, check out the eventsource-client package.
Installation
npm install --save eventsource
Supported engines
- Node.js >= 18
- Chrome >= 63
- Safari >= 11.3
- Firefox >= 65
- Edge >= 79
- Deno >= 1.30
- Bun >= 1.1.23
Basically, any environment that supports:
If you need to support older runtimes, try the 2.x branch/version range (note: 2.x branch is primarily targetted at Node.js, not browsers).
Usage
import {EventSource} from 'eventsource'
const es = new EventSource('https://my-server.com/sse')
/*
* This will listen for events with the field `event: notice`.
*/
es.addEventListener('notice', (event) => {
console.log(event.data)
})
/*
* This will listen for events with the field `event: update`.
*/
es.addEventListener('update', (event) => {
console.log(event.data)
})
/*
* The event "message" is a special case, as it will capture events _without_ an
* event field, as well as events that have the specific type `event: message`.
* It will not trigger on any other event type.
*/
es.addEventListener('message', (event) => {
console.log(event.data)
})
/**
* To explicitly close the connection, call the `close` method.
* This will prevent any reconnection from happening.
*/
setTimeout(() => {
es.close()
}, 10_000)
TypeScript
Make sure you have configured your TSConfig so it matches the environment you are targetting. If you are targetting browsers, this would be dom:
{
"compilerOptions": {
"lib": ["dom"],
},
}
If you're using Node.js, ensure you have @types/node installed (and it is version 18 or higher). Cloudflare workers have @cloudflare/workers-types etc.
The following errors are caused by targetting an environment that does not have the necessary types available:
error TS2304: Cannot find name 'Event'.
error TS2304: Cannot find name 'EventTarget'.
error TS2304: Cannot find name 'MessageEvent'.
Migrating from v1 / v2
See MIGRATION.md for a detailed migration guide.
Extensions to the WhatWG/W3C API
Message and code properties on errors
The error event has a message and code property that can be used to get more information about the error. In the specification, the Event
es.addEventListener('error', (err) => {
if (err.code === 401 || err.code === 403) {
console.log('not authorized')
}
})
Specify fetch implementation
The EventSource constructor accepts an optional fetch property in the second argument that can be used to specify the fetch implementation to use.
This can be useful in environments where the global fetch function is not available - but it can also be used to alter the request/response behaviour.
Setting HTTP request headers
const es = new EventSource('https://my-server.com/sse', {
fetch: (input, init) =>
fetch(input, {
...init,
headers: {
...init.headers,
Authorization: 'Bearer myToken',
},
}),
})
HTTP/HTTPS proxy
Use a package like node-fetch-native to add proxy support, either through environment variables or explicit configuration.
// npm install node-fetch-native --save
import {fetch} from 'node-fetch-native/proxy'
const es = new EventSource('https://my-server.com/sse', {
fetch: (input, init) => fetch(input, init),
})
Allow unauthorized HTTPS requests
Use a package like undici for more control of fetch options through the use of an Agent.
// npm install undici --save
import {fetch, Agent} from 'undici'
await fetch('https://my-server.com/sse', {
dispatcher: new Agent({
connect: {
rejectUnauthorized: false,
},
}),
})
License
MIT-licensed. See LICENSE.