<p>
An <code>Event</code> is an object
that allows you to be notified
when something interesting happens.
Here's an example of using the
<code>chrome.tabs.onCreated</code> event
to be notified whenever there's a new tab:
</p>

<pre>
chrome.tabs.onCreated.<b>addListener(function(</b>tab<b>) {</b>
  appendToLog('tabs.onCreated --'
              + ' window: ' + tab.windowId
              + ' tab: '    + tab.id
              + ' index: '  + tab.index
              + ' url: '    + tab.url);
<b>});</b>
</pre>

<p>
As the example shows,
you register for notification using <code>addListener()</code>.
The argument to <code>addListener()</code>
is always a function that you define to handle the event,
but the parameters to the function depend on
which event you're handling.
Checking the documentation for
<a href="tabs.html#event-onCreated"><code>chrome.tabs.onCreated</code></a>,
you can see that the function has a single parameter:
a <a href="tabs.html#type-Tab">Tab</a> object
that has details about the newly created tab.
</p>

<h2>
Methods
</h2>

<p>
You can invoke the following methods on any <code>Event</code> object:
</p>

<pre>
void addListener(function callback(...))
void removeListener(function callback(...))
bool hasListener(function callback(...))
</pre>

<!-- [PENDING: explain removeListener and hasListener] -->