Event.eventPhase

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2021.

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

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`, then `Document`, then the `HTMLHtmlElement`, 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`. 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

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