Revision 834315 of EventSource

<p>{{APIRef("Websockets API")}}</p>

<p>The <code>EventSource</code> interface is used to receive server-sent events. It connects to a server over HTTP and receives events in <code>text/event-stream</code> format without closing the connection.</p>

<p><span style="line-height:1.5">You can set the <code>onmessage</code> attribute to a JavaScript function to receive non-typed messages (that is, messages with no </span><code style="font-size: 14px;">event</code><span style="line-height:1.5"> field). You can also call </span><code style="font-size: 14px;">addEventListener()</code><span style="line-height:1.5"> to listen for events just like any other event source.</span></p>

<p>See <a href="/en/Server-sent_events/Using_server-sent_events" title="en/Server-sent events/Using server-sent events">Using server-sent events</a> for further details.</p>

<h2 id="Method_overview" name="Method_overview">Method overview</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <td><code>void <a href="#close()">close</a>();</code></td>
  </tr>
  <tr>
   <td><code>void <a href="#init()">init</a>(in nsIPrincipal principal, in nsIScriptContext scriptContext, in nsPIDOMWindow ownerWindow, in DOMString url);</code> {{ noscript_inline() }}</td>
  </tr>
 </tbody>
</table>

<h2 id="Attributes" name="Attributes">Properties</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <td class="header">Attribute</td>
   <td class="header">Type</td>
   <td class="header">Description</td>
  </tr>
  <tr>
   <td><code>onerror</code></td>
   <td><code>{{ Interface("nsIDOMEventListener") }}</code></td>
   <td>A JavaScript function to call when an error occurs.</td>
  </tr>
  <tr>
   <td><code>onmessage</code></td>
   <td><code>{{ Interface("nsIDOMEventListener") }}</code></td>
   <td>A JavaScript function to call when an a message without an <code>event</code> field arrives.</td>
  </tr>
  <tr>
   <td><code>onopen</code></td>
   <td><code>{{ Interface("nsIDOMEventListener") }}</code></td>
   <td>A JavaScript function to call when the connection has opened.</td>
  </tr>
  <tr>
   <td><code>readyState</code></td>
   <td><code><a href="/en/long" title="en/long">long</a></code></td>
   <td>The state of the connection, must be one of <code>CONNECTING</code>, <code>OPEN</code>, or <code>CLOSED</code>. <strong>Read only.</strong></td>
  </tr>
  <tr>
   <td><code>url</code></td>
   <td>{{ domxref("DOMString") }}</td>
   <td><strong>Read only.</strong></td>
  </tr>
 </tbody>
</table>

<p>In addition to these exposed attributes, there are two internal attributes that are not exposed directly:</p>

<dl>
 <dt>reconnection time</dt>
 <dd>This is a time, in milliseconds, used to determine how long to wait after a failed attempt to connect before trying again.</dd>
 <dt>last event ID&nbsp;string</dt>
 <dd>This is initially the empty string; the server can send a message with the field name <code>id</code> to set this value.</dd>
</dl>

<h2 id="Constants" name="Constants">Constants</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <td class="header">Constant</td>
   <td class="header">Value</td>
   <td class="header">Description</td>
  </tr>
  <tr>
   <td><code>CONNECTING</code></td>
   <td><code>0</code></td>
   <td>The connection is being established.</td>
  </tr>
  <tr>
   <td><code>OPEN</code></td>
   <td><code>1</code></td>
   <td>The connection is open and dispatching events.</td>
  </tr>
  <tr>
   <td><code>CLOSED</code></td>
   <td><code>2</code></td>
   <td>The connection is not being established, has been closed or there was a fatal error.</td>
  </tr>
 </tbody>
</table>

<h2 id="Methods" name="Methods">Methods</h2>

<h3 id="close()" name="close()">close()</h3>

<p>Closes the connection, if any, and sets the <code>readyState</code> attribute to <code>CLOSED</code>. If the connection is already closed, the method does nothing.</p>

<pre class="eval">
void close();
</pre>

<h6 id="Parameters" name="Parameters">Parameters</h6>

<p>None.</p>

<p>{{ method_noscript("init") }}</p>

<p>Initializes the object for use from C++ code with the principal, script context, and owner window that should be used.</p>

<pre class="eval">
void init(
  in nsIPrincipal principal,
  in nsIScriptContext scriptContext,
  in nsPIDOMWindow ownerWindow,
  in DOMString url
);
</pre>

<h6 id="Parameters" name="Parameters">Parameters</h6>

<dl>
 <dt><code>principal</code></dt>
 <dd>The principal to use for the request. This must not be <code>null</code>.</dd>
 <dt><code>scriptContext</code></dt>
 <dd>The script context to use for the request. May be <code>null</code>.</dd>
 <dt><code>ownerWindow</code></dt>
 <dd>The associated window for the request. May be <code>null</code>.</dd>
 <dt><code>url</code></dt>
 <dd>The <code>EventSource</code>'s URL. This must not be empty.</dd>
</dl>

<h2 id="See_also" name="See_also">See also</h2>

<ul>
 <li>{{ spec("https://html.spec.whatwg.org/multipage/comms.html#the-eventsource-interface","Server-Sent Events: The EventSource Interface","CR") }}</li>
 <li><a href="/en/Server-sent_events/Using_server-sent_events" title="en/Server-sent events/Using server-sent events">Using server-sent events</a></li>
</ul>

<h2 id="Browser_compatibility">Browser compatibility</h2>

<p>{{ CompatibilityTable() }}</p>

<div id="compat-desktop">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Chrome</th>
   <th>Firefox (Gecko)</th>
   <th>Internet Explorer</th>
   <th>Opera</th>
   <th>Safari</th>
  </tr>
  <tr>
   <td>EventSource support</td>
   <td>9</td>
   <td>{{ CompatGeckoDesktop("6.0") }}</td>
   <td>{{ CompatUnknown() }}</td>
   <td>11</td>
   <td>5</td>
  </tr>
  <tr>
   <td>CORS&nbsp;support</td>
   <td>26</td>
   <td>{{ CompatGeckoDesktop("11.0") }}</td>
   <td>{{ CompatUnknown() }}</td>
   <td>12</td>
   <td>{{ CompatUnknown() }}</td>
  </tr>
 </tbody>
</table>
</div>

<div id="compat-mobile">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Android</th>
   <th>Firefox Mobile (Gecko)</th>
   <th>IE Mobile</th>
   <th>Opera Mobile</th>
   <th>Safari Mobile</th>
  </tr>
  <tr>
   <td>EventSource support</td>
   <td>{{ CompatAndroid("4.4") }}</td>
   <td>{{ CompatUnknown() }}</td>
   <td>{{CompatUnknown()}}</td>
   <td>{{ CompatUnknown() }}</td>
   <td>{{ CompatUnknown() }}</td>
  </tr>
 </tbody>
</table>
</div>

<p>&nbsp;</p>