event-source-polyfill

What is event-source-polyfill?

The event-source-polyfill package provides a polyfill for the EventSource API, which is used for receiving server-sent events (SSE). This is particularly useful for environments that do not natively support EventSource, such as older browsers or certain server-side JavaScript environments.

What are event-source-polyfill's main functionalities?

Basic EventSource Polyfill

This code demonstrates how to use the event-source-polyfill to create an EventSource instance that listens for server-sent events from a specified URL. It sets up handlers for incoming messages and errors.

const EventSource = require('event-source-polyfill');

const es = new EventSource('http://example.com/events');

es.onmessage = function(event) {
  console.log('New message:', event.data);
};

es.onerror = function(error) {
  console.error('Error:', error);
};

Custom Event Handlers

This code shows how to add custom event listeners for specific event types using the event-source-polyfill. In this example, a custom event named 'customEvent' is handled.

const EventSource = require('event-source-polyfill');

const es = new EventSource('http://example.com/events');

es.addEventListener('customEvent', function(event) {
  console.log('Custom event received:', event.data);
});

es.onerror = function(error) {
  console.error('Error:', error);
};

Reconnection Logic

This code demonstrates how to handle reconnection logic using the event-source-polyfill. It listens for errors and attempts to reconnect if the connection is closed.

const EventSource = require('event-source-polyfill');

const es = new EventSource('http://example.com/events', { withCredentials: true });

es.onopen = function() {
  console.log('Connection opened');
};

es.onmessage = function(event) {
  console.log('New message:', event.data);
};

es.onerror = function(error) {
  console.error('Error:', error);
  if (es.readyState === EventSource.CLOSED) {
    console.log('Reconnecting...');
    es = new EventSource('http://example.com/events', { withCredentials: true });
  }
};

Other packages similar to event-source-polyfill

eventsource

The eventsource package is a pure JavaScript implementation of the EventSource client for Node.js. It provides similar functionality to event-source-polyfill but is specifically designed for server-side use in Node.js environments.

sse

The sse package is a lightweight library for handling server-sent events in Node.js. It offers a simple API for creating and managing EventSource connections, similar to event-source-polyfill, but is more focused on server-side implementations.

eventsource-polyfill

The eventsource-polyfill package is another polyfill for the EventSource API, similar to event-source-polyfill. It aims to provide compatibility for environments that do not natively support EventSource, with a focus on both client-side and server-side use cases.

README

EventSource polyfill - https://html.spec.whatwg.org/multipage/server-sent-events.html#server-sent-events

Installing:

You can get the code from npm or bower:

npm install event-source-polyfill

bower install event-source-polyfill

Just include src/eventsource.js or src/eventsource.min.js in your page to use the polyfill.

Ionic2/Angular2 Installation:

Unless a typescript definition file is created for this polyfill, this is how you would use it in an Ionic2 project. It should (in theory) be very similar in an Angular2 project.

npm install event-source-polyfill

Add to (or create) src/app/polyfills.ts (path is relative to where polyfills.ts is) :

import 'path/to/event-source-polyfill/src/eventsource.min.js'

Add anywhere you need access to EventSourcePolyfill class :

declare var EventSourcePolyfill: any;

Usage with webpack/browserify:

import { NativeEventSource, EventSourcePolyfill } from 'event-source-polyfill';

const EventSource = NativeEventSource || EventSourcePolyfill;
// OR: may also need to set as global property
global.EventSource =  NativeEventSource || EventSourcePolyfill;

Browser support:

• IE 10+, Firefox 3.5+, Chrome 3+, Safari 4+, Opera 12+
• IE 8 - IE 9: XDomainRequest is used internally, which has some limitations (2KB padding is required, no way to send cookies, no way to use client certificates)
• It works on Mobile Safari, Opera Mobile, Chrome for Android, Firefox for Android
• It does not work on: Android Browser(requires 4 KB padding), Opera Mini

Advantages:

• Simple server-side code
• Cross-domain requests support

Server-side requirements:

• "Last-Event-ID" is sent in a query string (CORS + "Last-Event-ID" header is not supported by all browsers)
• It is required to send 2 KB padding for IE < 10 and Chrome < 13 at the top of the response stream (the polyfill sends padding=true query argument)
• You need to send "comment" messages each 15-30 seconds, these messages will be used as heartbeat to detect disconnects - see https://bugzilla.mozilla.org/show_bug.cgi?id=444328

Specification:

• http://www.w3.org/TR/eventsource/

Build:

• To build EventSource, just install npm modules (npm install) and then run the build (npm run build). It should generate a new version of src/eventsource.min.js.

Notes:

• If you are using HTTP Basic Authentication, you can embed credentials into the URL - http://username:[e-mail].

Custom Headers:

var es = new EventSourcePolyfill('/events', {
  headers: {
    'X-Custom-Header': 'value'
  }
});

Other EventSource polyfills:

• https://github.com/remy/polyfills/blob/master/EventSource.js by Remy Sharp
• https://github.com/rwldrn/jquery.eventsource by Rick Waldron
• https://github.com/amvtek/EventSource by AmvTek

EXAMPLE

server-side (node.js)

var PORT = 8081;

var http = require("http");
var fs = require("fs");
var url = require("url");

http.createServer(function (request, response) {
  var parsedURL = url.parse(request.url, true);
  var pathname = parsedURL.pathname;
  if (pathname === "/events.php") {

    response.writeHead(200, {
      "Content-Type": "text/event-stream",
      "Cache-Control": "no-store",
      "Access-Control-Allow-Origin": "*"
    });

    var padding = new Array(2049);
    response.write(":" + padding.join(" ") + "\n"); // 2kB padding for IE
    response.write("retry: 2000\n");

    var lastEventId = Number(request.headers["last-event-id"]) || Number(parsedURL.query.lastEventId) || 0;

    var timeoutId = 0;
    var i = lastEventId;
    var c = i + 100;
    var f = function () {
      if (++i < c) {
        response.write("id: " + i + "\n");
        response.write("data: " + i + "\n\n");
        timeoutId = setTimeout(f, 1000);
      } else {
        response.end();
      }
    };

    f();

    response.on("close", function () {
      clearTimeout(timeoutId);
    });

  } else {
    if (pathname === "/") {
      pathname = "/index.html";
    }
    if (pathname === "/index.html" || pathname === "../src/eventsource.js") {
      response.writeHead(200, {
        "Content-Type": pathname === "/index.html" ? "text/html" : "text/javascript"
      });
      response.write(fs.readFileSync(__dirname + pathname));
    }
    response.end();
  }
}).listen(PORT);

or use PHP (see php/events.php)

<?php

  header("Content-Type: text/event-stream");
  header("Cache-Control: no-store");
  header("Access-Control-Allow-Origin: *");

  $lastEventId = floatval(isset($_SERVER["HTTP_LAST_EVENT_ID"]) ? $_SERVER["HTTP_LAST_EVENT_ID"] : 0);
  if ($lastEventId == 0) {
    $lastEventId = floatval(isset($_GET["lastEventId"]) ? $_GET["lastEventId"] : 0);
  }

  echo ":" . str_repeat(" ", 2048) . "\n"; // 2 kB padding for IE
  echo "retry: 2000\n";

  // event-stream
  $i = $lastEventId;
  $c = $i + 100;
  while (++$i < $c) {
    echo "id: " . $i . "\n";
    echo "data: " . $i . ";\n\n";
    ob_flush();
    flush();
    sleep(1);
  }

?>

index.html (php/index.html):

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <title>EventSource example</title>
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <script src="../src/eventsource.js"></script>
    <script>
      var es = new EventSource("events.php");
      var listener = function (event) {
        var div = document.createElement("div");
        var type = event.type;
        div.appendChild(document.createTextNode(type + ": " + (type === "message" ? event.data : es.url)));
        document.body.appendChild(div);
      };
      es.addEventListener("open", listener);
      es.addEventListener("message", listener);
      es.addEventListener("error", listener);
    </script>
</head>
<body>
</body>
</html>

License

The MIT License (MIT)

Copyright (c) 2012 [e-mail]

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.