HTMLMediaElement: loadstart イベント

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

loadstart イベントは、ブラウザーがリソースの読み込みを開始したときに発生します。

構文

このイベントを addEventListener() などのメソッドで使用するか、イベントハンドラープロパティを設定するかしてください。

addEventListener("loadstart", (event) => {});

onloadstart = (event) => {};

イベント型

一般的な Event です。

例

ライブデモ

HTML

html

<div class="example">
  <button type="button">Load video</button>
  <video controls width="250"></video>

  <div class="event-log">
    <label for="eventLog">Event log:</label>
    <textarea readonly class="event-log-contents" id="eventLog"></textarea>
  </div>
</div>

.event-log-contents {
  width: 18rem;
  height: 5rem;
  border: 1px solid black;
  margin: 0.2rem;
  padding: 0.2rem;
}

.example {
  display: grid;
  grid-template-areas:
    "button log"
    "video  log";
}

button {
  grid-area: button;
  width: 10rem;
  margin: 0.5rem 0;
}

video {
  grid-area: video;
}

.event-log {
  grid-area: log;
}

.event-log > label {
  display: block;
}

JavaScript

const loadVideo = document.querySelector("button");
const video = document.querySelector("video");
const eventLog = document.querySelector(".event-log-contents");
let source = null;

function handleEvent(event) {
  eventLog.textContent += `${event.type}\n`;
}

video.addEventListener("loadstart", handleEvent);
video.addEventListener("progress", handleEvent);
video.addEventListener("canplay", handleEvent);
video.addEventListener("canplaythrough", handleEvent);

loadVideo.addEventListener("click", () => {
  if (source) {
    document.location.reload();
  } else {
    loadVideo.textContent = "Reset example";
    source = document.createElement("source");
    source.setAttribute("src", "/shared-assets/videos/flower.webm");
    source.setAttribute("type", "video/webm");

    video.appendChild(source);
  }
});

結果

仕様書

Specification
HTML # event-media-loadstart
HTML # handler-onloadstart