---
title: dragstart
slug: Web/API/Document/dragstart_event
tags:
  - DOM
  - dragstart
  - 事件
  - 拖动
translation_of: Web/API/Document/dragstart_event
---
<div>当用户开始拖动一个元素或者一个选择文本的时候 <code>dragstart</code> 事件就会触发。</div>

<h2 id="基本信息">基本信息</h2>

<table class="properties">
 <tbody>
  <tr>
   <td>Bubbles</td>
   <td>Yes</td>
  </tr>
  <tr>
   <td>Cancelable</td>
   <td>Yes</td>
  </tr>
  <tr>
   <td>Target objects</td>
   <td>{{domxref("Document")}}, {{domxref("Element")}}</td>
  </tr>
  <tr>
   <td>Interface</td>
   <td>{{domxref("DragEvent")}}</td>
  </tr>
  <tr>
   <td>Default Action</td>
   <td>Initiate the drag-and-drop operation.</td>
  </tr>
 </tbody>
</table>

<h2 id="属性">属性</h2>

<table class="standard-table">
 <thead>
  <tr>
   <th scope="col">Property</th>
   <th scope="col">Type</th>
   <th scope="col">Description</th>
  </tr>
 </thead>
 <tbody>
  <tr>
   <td><code>target</code> {{readonlyInline}}</td>
   <td><a href="/en-US/docs/Web/API/EventTarget" title="EventTarget is an interface implemented by objects that can receive events and may have listeners for them."><code>EventTarget</code></a></td>
   <td>The element that was underneath the element being dragged.</td>
  </tr>
  <tr>
   <td><code>type</code> {{readonlyInline}}</td>
   <td><a href="/en-US/docs/Web/API/DOMString" title="DOMString is a UTF-16 String. As JavaScript already uses such strings, DOMString is mapped directly to a String."><code>DOMString</code></a></td>
   <td>The type of event.</td>
  </tr>
  <tr>
   <td><code>bubbles</code> {{readonlyInline}}</td>
   <td><a href="/en-US/docs/Web/API/Boolean" title="The Boolean object is an object wrapper for a boolean value."><code>Boolean</code></a></td>
   <td>Whether the event normally bubbles or not</td>
  </tr>
  <tr>
   <td><code>cancelable</code> {{readonlyInline}}</td>
   <td><a href="/en-US/docs/Web/API/Boolean" title="The Boolean object is an object wrapper for a boolean value."><code>Boolean</code></a></td>
   <td>Whether the event is cancellable or not?</td>
  </tr>
  <tr>
   <td><code>view</code> {{readonlyInline}}</td>
   <td><a class="new" href="/en-US/docs/Web/API/WindowProxy" rel="nofollow" title="The documentation about this has not yet been written; please consider contributing!"><code>WindowProxy</code></a></td>
   <td><a href="/en-US/docs/Web/API/Document/defaultView" title="In browsers, document.defaultView returns the window object associated with a document, or null if none is available."><code>document.defaultView</code></a> (<code>window</code> of the document)</td>
  </tr>
  <tr>
   <td><code>detail</code> {{readonlyInline}}</td>
   <td><code>long</code> (<code>float</code>)</td>
   <td>0.</td>
  </tr>
  <tr>
   <td><code>dataTransfer</code></td>
   <td>DataTransfer</td>
   <td>The data that underlies a drag-and-drop operation, known as the <a href="/en-US/docs/Web/API/DataTransfer">drag data store</a>. Protected mode.</td>
  </tr>
  <tr>
   <td><code>currentTarget</code> {{readonlyInline}}</td>
   <td>EventTarget</td>
   <td>The node that had the event listener attached.</td>
  </tr>
  <tr>
   <td><code>relatedTarget</code> {{readonlyInline}}</td>
   <td>EventTarget</td>
   <td>For <code>mouseover</code>, <code>mouseout</code>, <code>mouseenter</code> and <code>mouseleave</code> events: the target of the complementary event (the <code>mouseleave</code> target in the case of a <code>mouseenter</code> event). <code>null</code> otherwise.</td>
  </tr>
  <tr>
   <td><code>screenX</code> {{readonlyInline}}</td>
   <td>long</td>
   <td>The X coordinate of the mouse pointer in global (screen) coordinates.</td>
  </tr>
  <tr>
   <td><code>screenY</code> {{readonlyInline}}</td>
   <td>long</td>
   <td>The Y coordinate of the mouse pointer in global (screen) coordinates.</td>
  </tr>
  <tr>
   <td><code>clientX</code> {{readonlyInline}}</td>
   <td>long</td>
   <td>The X coordinate of the mouse pointer in local (DOM content) coordinates.</td>
  </tr>
  <tr>
   <td><code>clientY</code> {{readonlyInline}}</td>
   <td>long</td>
   <td>The Y coordinate of the mouse pointer in local (DOM content) coordinates.</td>
  </tr>
  <tr>
   <td><code>button</code> {{readonlyInline}}</td>
   <td>unsigned short</td>
   <td>The button number that was pressed when the mouse event was fired: Left button=0, middle button=1 (if present), right button=2. For mice configured for left handed use in which the button actions are reversed the values are instead read from right to left.</td>
  </tr>
  <tr>
   <td><code>buttons</code> {{readonlyInline}}</td>
   <td>unsigned short</td>
   <td>The buttons being pressed when the mouse event was fired: Left button=1, Right button=2, Middle (wheel) button=4, 4th button (typically, "Browser Back" button)=8, 5th button (typically, "Browser Forward" button)=16. If two or more buttons are pressed, returns the logical sum of the values. E.g., if Left button and Right button are pressed, returns 3 (=1 | 2). <a href="/en-US/docs/Web/API/MouseEvent">More info</a>.</td>
  </tr>
  <tr>
   <td><code>mozPressure</code> {{readonlyInline}}</td>
   <td>float</td>
   <td>The amount of pressure applied to a touch or tabdevice when generating the event; this value ranges between 0.0 (minimum pressure) and 1.0 (maximum pressure).</td>
  </tr>
  <tr>
   <td><code>ctrlKey</code> {{readonlyInline}}</td>
   <td>boolean</td>
   <td><code>true</code> if the control key was down when the event was fired. <code>false</code> otherwise.</td>
  </tr>
  <tr>
   <td><code>shiftKey</code> {{readonlyInline}}</td>
   <td>boolean</td>
   <td><code>true</code> if the shift key was down when the event was fired. <code>false</code> otherwise.</td>
  </tr>
  <tr>
   <td><code>altKey</code> {{readonlyInline}}</td>
   <td>boolean</td>
   <td><code>true</code> if the alt key was down when the event was fired. <code>false</code> otherwise.</td>
  </tr>
  <tr>
   <td><code>metaKey</code> {{readonlyInline}}</td>
   <td>boolean</td>
   <td><code>true</code> if the meta key was down when the event was fired. <code>false</code> otherwise.</td>
  </tr>
 </tbody>
</table>

<h2 id="示例：dropzone" name="示例：dropzone">示例：dropzone</h2>

<h3 id="HTML_内容">HTML 内容</h3>

<pre class="brush: html">&lt;div class="dropzone"&gt;
    &lt;div id="draggable" draggable="true" ondragstart="event.dataTransfer.setData('text/plain',null)"&gt;
        This div is draggable
    &lt;/div&gt;
&lt;/div&gt;
&lt;div class="dropzone"&gt;&lt;/div&gt;
&lt;div class="dropzone"&gt;&lt;/div&gt;
&lt;div class="dropzone"&gt;&lt;/div&gt;</pre>

<h3 id="CSS_内容">CSS 内容</h3>

<pre class="brush: css">  #draggable {
    width: 200px;
    height: 20px;
    text-align: center;
    background: white;
  }

  .dropzone {
    width: 200px;
    height: 20px;
    background: blueviolet;
    margin-bottom: 10px;
    padding: 10px;
  }</pre>

<h3 id="JavaScript_内容">JavaScript 内容</h3>

<pre class="brush: js">  var dragged;

  /* 可拖动的目标元素会触发事件 */
  document.addEventListener("drag", function( event ) {

  }, false);

  document.addEventListener("dragstart", function( event ) {
      // 保存拖动元素的引用(ref.)
      dragged = event.target;
      // 使其半透明
      event.target.style.opacity = .5;
  }, false);

  document.addEventListener("dragend", function( event ) {
      // 重置透明度
      event.target.style.opacity = "";
  }, false);

  /* 放下目标节点时触发事件 */
  document.addEventListener("dragover", function( event ) {
      // 阻止默认动作
      event.preventDefault();
  }, false);

  document.addEventListener("dragenter", function( event ) {
      // 当可拖动的元素进入可放置的目标高亮目标节点
      if ( event.target.className == "dropzone" ) {
          event.target.style.background = "purple";
      }

  }, false);

  document.addEventListener("dragleave", function( event ) {
      // 当拖动元素离开可放置目标节点，重置其背景
      if ( event.target.className == "dropzone" ) {
          event.target.style.background = "";
      }

  }, false);

  document.addEventListener("drop", function( event ) {
      // 阻止默认动作（如打开一些元素的链接）
      event.preventDefault();
      // 移动拖动的元素到所选择的放置目标节点
      if ( event.target.className == "dropzone" ) {
          event.target.style.background = "";
          dragged.parentNode.removeChild( dragged );
          event.target.appendChild( dragged );
      }

  }, false);</pre>

<p>{{ EmbedLiveSample('示例：dropzone') }}</p>

<h2 id="浏览器支持">浏览器支持</h2>

<div>{{CompatibilityTable}}</div>

<div id="compat-desktop">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Chrome</th>
   <th>Firefox (Gecko)</th>
   <th>Internet Explorer</th>
   <th>Opera</th>
   <th>Safari (WebKit)</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>4</td>
   <td>{{CompatGeckoDesktop("1.9.1")}}</td>
   <td>10</td>
   <td>12</td>
   <td>3.1</td>
  </tr>
 </tbody>
</table>
</div>

<div id="compat-mobile">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Android</th>
   <th>Android Webview</th>
   <th>Chrome for Android</th>
   <th>Firefox Mobile (Gecko)</th>
   <th>Firefox OS</th>
   <th>IE Mobile</th>
   <th>Opera Mobile</th>
   <th>Safari Mobile</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatIE("10")}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
  </tr>
 </tbody>
</table>
</div>

<h2 id="相关事件">相关事件</h2>

<ul>
 <li>{{event("drag")}}</li>
 <li>{{event("dragstart")}}</li>
 <li>{{event("dragend")}}</li>
 <li>{{event("dragover")}}</li>
 <li>{{event("dragenter")}}</li>
 <li>{{event("dragleave")}}</li>
 <li>{{event("dragexit")}}</li>
 <li>{{event("drop")}}</li>
</ul>