Event.eventPhase

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

Browser compatibility

BCD tables only load in the browser