From 322c7b894df365d38a1279ac181bfcc99950d42d Mon Sep 17 00:00:00 2001
From: Wyatt <854185073@qq.com>
Date: Mon, 13 Dec 2021 21:24:33 +0800
Subject: Add Web/API/HTMLElement/transitionstart_event, zh-CN (#3309)

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+---
+title: 'HTMLElement: transitionstart 事件'
+slug: Web/API/HTMLElement/transitionstart_event
+tags:
+  - CSS Transitions
+  - 事件
+  - HTML DOM
+  - HTMLElement
+  - 参考
+  - TransitionEvent
+  - transitionstart
+browser-compat: api.HTMLElement.transitionstart_event
+---
+{{APIRef}}{{SeeCompatTable}}
+
+**`transitionstart`** 事件会在 [CSS transition](/en-US/docs/Web/CSS/CSS_Transitions/Using_CSS_transitions) 实际开始的时候触发， 或者说在某个 {{cssxref("transition-delay")}} 已经结束之后触发。
+
+<table class="properties">
+  <tbody>
+    <tr>
+      <th scope="row">是否冒泡</th>
+      <td>是</td>
+    </tr>
+    <tr>
+      <th scope="row">是否可取消</th>
+      <td>否</td>
+    </tr>
+    <tr>
+      <th scope="row">接口</th>
+      <td>{{domxref("TransitionEvent")}}</td>
+    </tr>
+    <tr>
+      <th scope="row">事件处理器属性</th>
+      <td>
+        {{domxref("GlobalEventHandlers/ontransitionstart", "ontransitionstart")}}
+      </td>
+    </tr>
+  </tbody>
+</table>
+
+## 示例
+
+下列代码对 `transitionstart` 事件添加了一个监听器：
+
+```js
+element.addEventListener('transitionstart', () => {
+  console.log('transition 开始');
+});
+```
+
+一样的代码，但是使用 [`ontransitionstart`](/en-US/docs/Web/API/GlobalEventHandlers/ontransitionstart) 属性来替代 `addEventListener()`：
+
+```js
+element.ontransitionstart = () => {
+  console.log('transition 开始');
+};
+```
+
+### 运行实例
+
+在下面的例子中，我们有一个简单的 {{htmlelement("div")}} 元素，并设置了一个包含 delay 的 transition 样式。
+
+```html
+<div class="transition">Hover over me</div>
+<div class="message"></div>
+```
+
+```css
+.transition {
+  width: 100px;
+  height: 100px;
+  background: rgba(255,0,0,1);
+  transition-property: transform, background;
+  transition-duration: 2s;
+  transition-delay: 1s;
+}
+
+.transition:hover {
+  transform: rotate(90deg);
+  background: rgba(255,0,0,0);
+}
+```
+
+对此，我们再添加一些 JavaScript 代码来指出 {{domxref("HTMLElement/transitionstart_event", "transitionstart")}} 和 {{domxref("HTMLElement/transitionrun_event", "transitionrun")}} 事件在哪里触发。
+
+```js
+const transition = document.querySelector('.transition');
+const message = document.querySelector('.message');
+
+transition.addEventListener('transitionrun', function() {
+  message.textContent = 'transitionrun 触发了';
+});
+
+transition.addEventListener('transitionstart', function() {
+  message.textContent = 'transitionstart 触发了';
+});
+
+transition.addEventListener('transitionend', function() {
+  message.textContent = 'transitionend 触发了';
+});
+```
+
+{{ EmbedLiveSample('Examples', '100%', '150px') }}
+
+不同的地方是：
+
+- transitionrun 在 transition 创建的时候被触发。（或者说在某个 delay 开始的时候）
+- transitionstart 在动画实际开始的时候被触发。 (或者说在某个 delay 结束的时候)
+
+## 规范
+
+{{Specifications}}
+
+## 浏览器兼容性
+
+{{Compat}}
+
+## 参见
+
+- {{domxref("GlobalEventHandlers.ontransitionstart")}} 事件处理器
+- {{domxref("TransitionEvent")}} 接口
+- CSS 属性: {{cssxref("transition")}}, {{cssxref("transition-delay")}}, {{cssxref("transition-duration")}}, {{cssxref("transition-property")}}, {{cssxref("transition-timing-function")}}
+- 相关的事件: {{domxref("HTMLElement/transitionend_event", "transitionend")}}, {{domxref("HTMLElement/transitionrun_event", "transitionrun")}}, {{domxref("HTMLElement/transitioncancel_event", "transitioncancel")}}
+- 在 {{domxref("Document")}} targets 上的此事件: {{domxref("Document/transitionstart_event", "transitionstart")}}
+- 在 {{domxref("Window")}} targets 上的此事件: {{domxref("Window/transitionstart_event", "transitionstart")}}
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