Comparison of Event Targets
===========================

### Event targets

It's easy to get confused about which target to examine when writing an event handler. This article should clarify the use of the target properties.

There are 5 targets to consider:

| Property | Defined in | Purpose |
| --- | --- | --- |
| event.target | DOM Event Interface | 
 The DOM element on the lefthand side of the call that triggered this
 event, eg:

```

*element*.dispatchEvent(*event*)
```

 |
| event.currentTarget | DOM Event Interface | 
 The
 `EventTarget`
 whose
 `EventListeners`
 are currently being processed. As the event capturing and bubbling
 occurs this value changes.
  |
| event.relatedTarget | DOM MouseEvent Interface | Identifies a secondary target for the event. |
| event.explicitOriginalTarget | Event.webidl | 
非标准
 If the event was retargeted for
 some reason other than an anonymous boundary crossing, this will be set
 to the target before the retargeting occurs. For example, mouse events
 are retargeted to their parent node when they happen over text nodes
 ([Firefox bug 185889](https://bugzil.la/185889)), and in that case `.target` will
 show the parent and `.explicitOriginalTarget` will show the
 text node.Unlike `.originalTarget`,
 `.explicitOriginalTarget` will never contain anonymous
 content.
  |
| event.originalTarget | Event.webidl | 
非标准
 The original target of the event,
 before any retargetings. See
 Anonymous Content#Event\_Flow\_and\_Targeting
 for details.
  |

### Use of `explicitOriginalTarget` and `originalTarget`

TODO: Only available in a Mozilla-based browser? TODO: Only suitable for extension-developers?

### Examples
```

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <title>Comparison of Event Targets</title>
    <style>
        table {
            border-collapse: collapse;
            height: 150px;
            width: 100%;
        }
        td {
            border: 1px solid #ccc;
            font-weight: bold;
            padding: 5px;
            min-height: 30px;
        }
        .standard {
            background-color: #99ff99;
        }
        .non-standard {
            background-color: #902D37;
        }
    </style>
</head>
<body>
    <table>
    <thead>
        <tr>
            <td class="standard">Original target dispatching the event <small>event.target</small></td>
            <td class="standard">Target who's event listener is being processed <small>event.currentTarget</small></td>
            <td class="standard">Identify other element (if any) involved in the event <small>event.relatedTarget</small></td>
            <td class="non-standard">If there was a retargetting of the event for some reason <small> event.explicitOriginalTarget</small> contains the target before retargetting (never contains anonymous targets)</td>
            <td class="non-standard">If there was a retargetting of the event for some reason <small> event.originalTarget</small> contains the target before retargetting (may contain anonymous targets)</td>
        </tr>
    </thead>
    <tr>
        <td id="target"></td>
        <td id="currentTarget"></td>
        <td id="relatedTarget"></td>
        <td id="explicitOriginalTarget"></td>
        <td id="originalTarget"></td>
    </tr>
</table>
<p>Clicking on the text will show the difference between explicitOriginalTarget, originalTarget and target</p>
<script>
    function handleClicks(e) {
        document.getElementById('target').innerHTML = e.target;
        document.getElementById('currentTarget').innerHTML = e.currentTarget;
        document.getElementById('relatedTarget').innerHTML = e.relatedTarget;
        document.getElementById('explicitOriginalTarget').innerHTML = e.explicitOriginalTarget;
        document.getElementById('originalTarget').innerHTML = e.originalTarget;
    }

    function handleMouseover(e) {
        document.getElementById('target').innerHTML = e.target;
        document.getElementById('relatedTarget').innerHTML = e.relatedTarget;
    }

    document.addEventListener('click', handleClicks, false);
    document.addEventListener('mouseover', handleMouseover, false);
</script>
</body>
</html>
```

### Use of `target` and `relatedTarget`

The `relatedTarget` property for the `mouseover` event holds the node that the mouse was previously over. For the `mouseout` event, it holds the node that the mouse moved to.

| Event type | event.target | event.relatedTarget |
| --- | --- | --- |
| `mouseover` | the EventTarget which the pointing device entered | the EventTarget which the pointing device exited |
| `mouseout` | the EventTarget which the pointing device exited | the EventTarget which the pointing device entered |

TODO: Also needs descriptions about `dragenter` and `dragexit` events.

#### Example
```

<hbox id="outer">
  <hbox id="inner"
        onmouseover="dump('mouseover ' + event.relatedTarget.id + ' > ' + event.target.id + '\n');"
        onmouseout="dump('mouseout  ' + event.target.id + ' > ' + event.relatedTarget.id + '\n');"
        style="margin: 100px; border: 10px solid black; width: 100px; height: 100px;" />
</hbox>
```