HTML ondragenter事件用法及代码示例

当可拖动元素输入有效的放置目标时，将发生HTML DOM ondragenter事件。

ondragenter和ondragleave事件可以帮助用户了解放置区。

在拖放操作的不同阶段中使用并发生了一些事件：

ondragstart:开始拖动元素时发生。
ondrag:在元素拖动时发生。
ondragend:元素拖动完成时发生。

ondragenter:当拖动的元素进入放置目标时发生。
ondragover:当拖动的元素在放置目标上方时发生。
ondragleave:当拖动的元素从放置目标离开时发生。
ondrop:当拖动的元素放置在放置目标上时发生。

用法:

在HTML中：
```
<element ondragenter="myScript">
```

在JavaScript中：

object.ondragenter = function(){myScript};

在JavaScript中，使用addEventListener()方法：
```
object.addEventListener("dragenter", myScript);
```

范例1：

<!DOCTYPE HTML> 
<html> 
  
<head> 
    <title> 
      HTML DOM ondrop Event 
  </title> 
    <style> 
        .droptarget { 
            float:center; 
            width:300px; 
            height:50px; 
            margin:20px; 
            padding:5px; 
            border:6px solid green; 
        } 
    </style> 
</head> 
  
<body> 
    <center> 
        <h1 style="color:green"> 
        GeeksforGeeks 
    </h1> 
        <h2>HTML DOM ondrop Event</h2> 
  
        <div class="droptarget" 
             ondrop="Eledrop(event)" 
             ondragenter="EledragEnter(event)" 
             ondragleave="EledragLeave(event)" 
             ondragover="EleallowDrop(event)"> 
  
            <p ondragstart="EledragStart(event)" 
               draggable="true"
               id="dragtarget"> 
                Dragable element 
            </p> 
        </div> 
  
        <div class="droptarget" 
             ondragenter="EledragEnter(event)"
             ondragleave="EledragLeave(event)" 
             ondrop="Eledrop(event)" 
             ondragover="EleallowDrop(event)"> 
        </div> 
  
        <p id="demo"></p> 
  
        <script> 
            function EledragStart(event) { 
                event.dataTransfer.setData("Text", event.target.id); 
            } 
  
            function EledragEnter(event) { 
                if (event.target.className == "droptarget") { 
                    document.getElementById( 
                      "demo").innerHTML = "Entered the dropzone"; 
                    event.target.style.border = "6px dotted red"; 
                } 
            } 
  
            function EledragLeave(event) { 
                if (event.target.className == "droptarget") { 
                    document.getElementById( 
                      "demo").innerHTML = "Left the dropzone"; 
                    event.target.style.border = ""; 
                } 
            } 
  
            function EleallowDrop(event) { 
                event.preventDefault(); 
            } 
  
            function Eledrop(event) { 
                event.preventDefault(); 
                var data = event.dataTransfer.getData("Text"); 
                event.target.appendChild(document.getElementById(data)); 
            } 
        </script> 
  </center> 
</body> 
  
</html>

输出：

范例2：

<!DOCTYPE HTML> 
<html> 
  
<head> 
    <title> 
        HTML DOM ondrop Event 
    </title> 
    <style> 
        .droptarget { 
            float:center; 
            width:300px; 
            height:50px; 
            margin:20px; 
            padding:5px; 
            border:6px solid green; 
        } 
    </style> 
</head> 
  
<body> 
    <center> 
        <h1 style="color:green"> 
        GeeksforGeeks 
    </h1> 
        <h2>HTML DOM ondrop Event</h2> 
  
        <div class="droptarget"> 
            <p draggable="true"
               id="dragtarget"> 
                Draggable Element 
            </p> 
        </div> 
  
        <div class="droptarget"></div> 
  
        <p id="demo"></p> 
  
        <script> 
            // Event fired on the drag target  
            document.ondragstart = function(event) { 
                event.dataTransfer.setData("Text", event.target.id); 
            }; 
  
            // Events fired on the drop target 
            document.ondragenter = function(event) { 
                if (event.target.className == "droptarget") { 
                    document.getElementById( 
                      "demo").innerHTML = "Entered the dropzone"; 
                    event.target.style.backgroundColor = "yellow"; 
                } 
            }; 
  
            document.ondragover = function(event) { 
                event.preventDefault(); 
            }; 
  
            document.ondragleave = function(event) { 
                if (event.target.className == "droptarget") { 
                    document.getElementById( 
                      "demo").innerHTML = "Left the dropzone"; 
                    event.target.style.backgroundColor = ""; 
                } 
            }; 
  
            document.ondrop = function(event) { 
                event.preventDefault(); 
                if (event.target.className == "droptarget") { 
                    event.target.style.backgroundColor = ""; 
                    var data = event.dataTransfer.getData("Text"); 
                    event.target.appendChild(document.getElementById(data)); 
                } 
            }; 
        </script> 
    </center> 
  
</body> 
  
</html>

输出：

范例3：

<!DOCTYPE HTML> 
<html> 
  
<head> 
    <title>HTML DOM ondrop Event</title> 
    <style> 
        .droptarget { 
            float:center; 
            width:300px; 
            height:50px; 
            margin:20px; 
            padding:5px; 
            border:6px solid green; 
        } 
    </style> 
</head> 
  
<body> 
    <center> 
        <h1 style="color:green"> 
        GeeksforGeeks 
    </h1> 
        <h2>HTML DOM ondrop Event</h2> 
  
        <div class="droptarget"> 
            <p draggable="true"
               id="dragtarget"> 
                Draggable Element 
            </p> 
        </div> 
  
        <div class="droptarget"></div> 
  
        <p id="demo"></p> 
  
        <script> 
            document.addEventListener("dragstart", function(event) { 
                event.dataTransfer.setData("Text", event.target.id); 
            }); 
  
            document.addEventListener("dragenter", function(event) { 
                if (event.target.className == "droptarget") { 
                    document.getElementById("demo").innerHTML = 
                        "Entered the dropzone"; 
                    event.target.style.backgroundColor = "yellow"; 
                } 
            }); 
  
            document.addEventListener("dragover", function(event) { 
                event.preventDefault(); 
            }); 
  
            document.addEventListener("dragleave", function(event) { 
                if (event.target.className == "droptarget") { 
                    document.getElementById( 
                      "demo").innerHTML = "Left the dropzone"; 
                    event.target.style.backgroundColor = ""; 
                } 
            }); 
  
            document.addEventListener("drop", function(event) { 
                event.preventDefault(); 
                if (event.target.className == "droptarget") { 
                    event.target.style.backgroundColor = ""; 
                    var data = event.dataTransfer.getData("Text"); 
                    event.target.appendChild(document.getElementById(data)); 
                } 
            }); 
        </script> 
    </center> 
</body> 
  
</html>

输出：

支持的浏览器：下面列出了ondragenter Event支持的浏览器：

谷歌浏览器
IE浏览器
Firefox
苹果Safari
Opera

相关用法

注：本文由纯净天空筛选整理自Vijay Sirra大神的英文原创作品 HTML | DOM ondragenter Event。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。