Event: eventPhase property

Available in workers

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

Value

Returns an integer value which specifies the current evaluation phase of the event flow. Possible values are:

• Event.NONE (0)
  • : The event is not 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 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 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 bubbles is true. Event listeners registered for this phase are triggered during this process.

Example

HTML

<h4>Event Propagation Chain</h4>
<ul>
  <li>Click 'd1'</li>
  <li>Analyze 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;
const divInfo = document.getElementById("divInfo");
const divs = document.getElementsByTagName("div");
const chCapture = document.getElementById("chCapture");

chCapture.addEventListener("click", () => {
  removeListeners();
  addListeners();
  clearDivs();
});
clearDivs();
addListeners();

function removeListeners() {
  for (const div of divs) {
    if (div.id !== "divInfo") {
      div.removeEventListener("click", onDivClick, true);
      div.removeEventListener("click", onDivClick, false);
    }
  }
}

function addListeners() {
  for (const div of divs) {
    if (div.id !== "divInfo") {
      if (chCapture.checked) {
        div.addEventListener("click", onDivClick, true);
      } else {
        div.addEventListener("click", onDivClick, false);
        div.onmousemove = () => {
          clear = true;
        };
      }
    }
  }
}

function onDivClick(e) {
  if (clear) {
    clearDivs();
    clear = false;
  }
  if (e.eventPhase === 2) {
    e.currentTarget.style.backgroundColor = "red";
  }
  const level =
    ["none", "capturing", "target", "bubbling"][e.eventPhase] ?? "error";
  const para = document.createElement("p");
  para.textContent = `${e.currentTarget.id}; eventPhase: ${level}`;
  divInfo.appendChild(para);
}

function clearDivs() {
  for (let i = 0; i < divs.length; i++) {
    if (divs[i].id !== "divInfo") {
      divs[i].style.backgroundColor = i % 2 !== 0 ? "#f6eedb" : "#cceeff";
    }
  }
  divInfo.textContent = "";
}

Result

Specifications

Browser compatibility