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    2.0.2 • Public • Published

    EventSource npm versionNPM DownloadsDependencies


    This library is a pure JavaScript implementation of the EventSource client. The API aims to be W3C compatible.

    You can use it with Node.js or as a browser polyfill for browsers that don't have native EventSource support.


    npm install eventsource


    npm install
    node ./example/sse-server.js
    node ./example/sse-client.js    # Node.js client
    open http://localhost:8080      # Browser client - both native and polyfill
    curl http://localhost:8080/sse  # Enjoy the simplicity of SSE

    Browser Polyfill

    Just add example/eventsource-polyfill.js file to your web page:

    <script src=/eventsource-polyfill.js></script>

    Now you will have two global constructors:

    window.EventSource // Unchanged if browser has defined it. Otherwise, same as window.EventSourcePolyfill

    If you're using webpack or browserify you can of course build your own. (The example/eventsource-polyfill.js is built with webpack).

    Extensions to the W3C API

    Setting HTTP request headers

    You can define custom HTTP headers for the initial HTTP request. This can be useful for e.g. sending cookies or to specify an initial Last-Event-ID value.

    HTTP headers are defined by assigning a headers attribute to the optional eventSourceInitDict argument:

    var eventSourceInitDict = {headers: {'Cookie': 'test=test'}};
    var es = new EventSource(url, eventSourceInitDict);

    Allow unauthorized HTTPS requests

    By default, https requests that cannot be authorized will cause the connection to fail and an exception to be emitted. You can override this behaviour, along with other https options:

    var eventSourceInitDict = {https: {rejectUnauthorized: false}};
    var es = new EventSource(url, eventSourceInitDict);

    Note that for Node.js < v0.10.x this option has no effect - unauthorized HTTPS requests are always allowed.

    HTTP status code on error events

    Unauthorized and redirect error status codes (for example 401, 403, 301, 307) are available in the status property in the error event.

    es.onerror = function (err) {
      if (err) {
        if (err.status === 401 || err.status === 403) {
          console.log('not authorized');

    HTTP/HTTPS proxy

    You can define a proxy option for the HTTP request to be used. This is typically useful if you are behind a corporate firewall.

    var es = new EventSource(url, {proxy: ''});


    MIT-licensed. See LICENSE


    npm i eventsource

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