Event.eventPhase
================

表示事件物件目前於事件流（Event Flow）中傳遞的進度為哪一個階段。

語法
--


```js
var phase = event.eventPhase;
```


回傳一個整數值以代表目前事件於事件流中的傳遞階段，可能的值將於事件傳遞階段常數說明。

常數
--

### 事件傳遞階段常數

These values describe which phase the event flow is currently being evaluated.

| 常數 | 值 | 說明 |
| --- | --- | --- |
| `Event.NONE` Read only  | 0 | No event is being processed at this time. |
| `Event.CAPTURING_PHASE` Read only  | 1 | The event is being propagated through the target's ancestor objects. This process starts with the `Window` (en-US), then `Document` (en-US), then the `HTMLHtmlElement` (en-US), and so on through the elements until the target's parent is reached. Event listeners registered for capture mode when `EventTarget.addEventListener()` was called are triggered during this phase. |
| `Event.AT_TARGET` Read only  | 2 | The event has arrived at the event's target. Event listeners registered for this phase are called at this time. If `Event.bubbles` is false, processing the event is finished after this phase is complete. |
| `Event.BUBBLING_PHASE` Read only  | 3 | The event is propagating back up through the target's ancestors in reverse order, starting with the parent, and eventually reaching the containing `Window` (en-US). This is known as bubbling, and occurs only if `Event.bubbles` is `true`. Event listeners registered for this phase are triggered during this process. |

For more details, see section 3.1, Event dispatch and DOM event flow, of the DOM Level 3 Events specification.

範例
--

### HTML


```html
<h4>Event Propagation Chain</h4>
<ul>
  <li>Click 'd1'</li>
  <li>Analyse event propagation chain</li>
  <li>Click next div and repeat the experience</li>
  <li>Change Capturing mode</li>
  <li>Repeat the experience</li>
</ul>
<input type="checkbox" id="chCapture" />
<label for="chCapture">Use Capturing</label>
<div id="d1">
  d1
  <div id="d2">
    d2
    <div id="d3">
      d3
      <div id="d4">d4</div>
    </div>
  </div>
</div>
<div id="divInfo"></div>
```

### CSS


```css
div {
  margin: 20px;
  padding: 4px;
  border: thin black solid;
}

#divInfo {
  margin: 18px;
  padding: 8px;
  background-color: white;
  font-size: 80%;
}
```

### JavaScript


```js
var clear = false,
  divInfo = null,
  divs = null,
  useCapture = false;
window.onload = function () {
  divInfo = document.getElementById("divInfo");
  divs = document.getElementsByTagName("div");
  chCapture = document.getElementById("chCapture");
  chCapture.onclick = function () {
    RemoveListeners();
    AddListeners();
  };
  Clear();
  AddListeners();
};

function RemoveListeners() {
  for (var i = 0; i < divs.length; i++) {
    var d = divs[i];
    if (d.id != "divInfo") {
      d.removeEventListener("click", OnDivClick, true);
      d.removeEventListener("click", OnDivClick, false);
    }
  }
}

function AddListeners() {
  for (var i = 0; i < divs.length; i++) {
    var d = divs[i];
    if (d.id != "divInfo") {
      d.addEventListener("click", OnDivClick, false);
      if (chCapture.checked) d.addEventListener("click", OnDivClick, true);
      d.onmousemove = function () {
        clear = true;
      };
    }
  }
}

function OnDivClick(e) {
  if (clear) {
    Clear();
    clear = false;
  }
  if (e.eventPhase == 2) e.currentTarget.style.backgroundColor = "red";
  var level =
    e.eventPhase == 0
      ? "none"
      : e.eventPhase == 1
        ? "capturing"
        : e.eventPhase == 2
          ? "target"
          : e.eventPhase == 3
            ? "bubbling"
            : "error";
  divInfo.innerHTML += e.currentTarget.id + "; eventPhase: " + level + "<br/>";
}

function Clear() {
  for (var i = 0; i < divs.length; i++) {
    if (divs[i].id != "divInfo")
      divs[i].style.backgroundColor = i & 1 ? "#f6eedb" : "#cceeff";
  }
  divInfo.innerHTML = "";
}
```

規範
--

| Specification |
| --- |
| DOM Standard # ref-for-dom-event-eventphase③ |