当前位置：文江博客知识库 en-US 文档 Web API Event eventPhase

Event.eventPhase - Web APIs 编辑

The eventPhase read-only property of the Event interface indicates which phase of the event flow is currently being evaluated.

Syntax

let phase = event.eventPhase;

Value

Returns an integer value which specifies the current evaluation phase of the event flow. Possible values are listed in Event phase constants.

Constants

Event phase constants

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

Constant	Value	Description
`Event.NONE`	`0`	No event is being processed at this time.
`Event.CAPTURING_PHASE`	`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`	`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`	`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.

Example

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

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

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

JavaScript

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

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

function OnDivClick(e) {
  if (clear) {
    Clear()
    clear = false
  }
  if (e.eventPhase == 2)
    e.currentTarget.style.backgroundColor = 'red';
    const level =
        e.eventPhase == 0 ? "none" :
        e.eventPhase == 1 ? "capturing" :
        e.eventPhase == 2 ? "target" :
        e.eventPhase == 3 ? "bubbling" : "error";
    const p = document.createElement('p')
    p.textContent = `${e.currentTarget.id}; eventPhase: ${level}`;
    divInfo.appendChild(p);
}

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

Result

Specifications

Specification	Status	Comment
DOM The definition of 'Event.eventPhase' in that specification.	Living Standard
DOM4 The definition of 'Event.eventPhase' in that specification.	Obsolete
Document Object Model (DOM) Level 2 Events Specification The definition of 'Event.eventPhase' in that specification.	Obsolete	Initial definition