借助 HTML 拖放界面，Web 应用可以在网页上接受拖放的文件。在拖放操作期间，拖动的文件和目录项会分别与文件条目和目录条目相关联。将文件拖放到浏览器中有两种方法：现代和经典。
现代风
使用 File System Access API 的 DataTransferItem.getAsFileSystemHandle() 方法
如果拖动的项是文件，DataTransferItem.getAsFileSystemHandle() 方法会返回一个带有 FileSystemFileHandle 对象的 promise；如果拖动的项是目录，则返回带有 FileSystemDirectoryHandle 对象的 promise。通过这些句柄，您可以读取文件或选择写回这些句柄。请注意，拖放接口的 DataTransferItem.kind 将 "file" 用于文件和目录，而 File System Access API 的 FileSystemHandle.kind 将 "file" 用于文件和目录。"directory"
经典路线
使用非标准 DataTransferItem.webkitGetAsEntry() 方法
如果拖动数据项是文件，DataTransferItem.webkitGetAsEntry() 方法会返回 FileSystemFileEntry；如果项是目录，则返回 FileSystemDirectoryEntry。虽然您可以读取该文件或目录，但无法向其中回写。该方法的缺点不符合标准轨道，但其优点在于，它支持目录。
渐进式增强
以下代码段会在新式 File System Access API 的 DataTransferItem.getAsFileSystemHandle() 方法受支持时使用该方法，然后回退到非标准 DataTransferItem.webkitGetAsEntry() 方法，最后回退到经典的 DataTransferItem.getAsFile() 方法。请务必检查每个 handle 的类型，因为它可以是以下任何一种：
FileSystemDirectoryHandle（如果选择了新式代码路径）。- 如果选择了非标准代码路径，则为
FileSystemDirectoryEntry。
所有类型都具有 name 属性，因此可以正常记录数据，并且始终行之有效。
// Run feature detection.
const supportsFileSystemAccessAPI =
'getAsFileSystemHandle' in DataTransferItem.prototype;
const supportsWebkitGetAsEntry =
'webkitGetAsEntry' in DataTransferItem.prototype;
// This is the drag and drop zone.
const elem = document.querySelector('main');
// Prevent navigation.
elem.addEventListener('dragover', (e) => {
e.preventDefault();
});
// Visually highlight the drop zone.
elem.addEventListener('dragenter', (e) => {
elem.style.outline = 'solid red 1px';
});
// Visually unhighlight the drop zone.
elem.addEventListener('dragleave', (e) => {
elem.style.outline = '';
});
// This is where the drop is handled.
elem.addEventListener('drop', async (e) => {
// Prevent navigation.
e.preventDefault();
if (!supportsFileSystemAccessAPI && !supportsWebkitGetAsEntry) {
// Cannot handle directories.
return;
}
// Unhighlight the drop zone.
elem.style.outline = '';
// Prepare an array of promises…
const fileHandlesPromises = [...e.dataTransfer.items]
// …by including only files (where file misleadingly means actual file _or_
// directory)…
.filter((item) => item.kind === 'file')
// …and, depending on previous feature detection…
.map((item) =>
supportsFileSystemAccessAPI
// …either get a modern `FileSystemHandle`…
? item.getAsFileSystemHandle()
// …or a classic `FileSystemFileEntry`.
: item.webkitGetAsEntry(),
);
// Loop over the array of promises.
for await (const handle of fileHandlesPromises) {
// This is where we can actually exclusively act on the directories.
if (handle.kind === 'directory' || handle.isDirectory) {
console.log(`Directory: ${handle.name}`);
}
}
});
深入阅读
演示
HTML
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<title>How to drag and drop directories</title>
</head>
<body>
<main>
<h1>How to drag and drop directories</h1>
<p>Drag and drop one or multiple files or directories onto the page.</p>
<pre></pre>
</main>
</body>
</html>CSS
:root {
color-scheme: dark light;
box-sizing: border-box;
}
*,
*:before,
*:after {
box-sizing: inherit;
}
body {
margin: 0;
padding: 1rem;
font-family: system-ui, sans-serif;
line-height: 1.5;
min-height: 100vh;
display: flex;
flex-direction: column;
}
img,
video {
height: auto;
max-width: 100%;
}
main {
flex-grow: 1;
}
footer {
margin-top: 1rem;
border-top: solid CanvasText 1px;
font-size: 0.8rem;
}
JS
const supportsFileSystemAccessAPI =
"getAsFileSystemHandle" in DataTransferItem.prototype;
const supportsWebkitGetAsEntry =
"webkitGetAsEntry" in DataTransferItem.prototype;
const elem = document.querySelector("main");
const debug = document.querySelector("pre");
elem.addEventListener("dragover", (e) => {
// Prevent navigation.
e.preventDefault();
});
elem.addEventListener("dragenter", (e) => {
elem.style.outline = "solid red 1px";
});
elem.addEventListener("dragleave", (e) => {
elem.style.outline = "";
});
elem.addEventListener("drop", async (e) => {
e.preventDefault();
elem.style.outline = "";
const fileHandlesPromises = [...e.dataTransfer.items]
.filter((item) => item.kind === "file")
.map((item) =>
supportsFileSystemAccessAPI
? item.getAsFileSystemHandle()
: supportsWebkitGetAsEntry
? item.webkitGetAsEntry()
: item.getAsFile()
);
for await (const handle of fileHandlesPromises) {
if (handle.kind === "directory" || handle.isDirectory) {
console.log(`Directory: ${handle.name}`);
debug.textContent += `Directory: ${handle.name}\n`;
} else {
console.log(`File: ${handle.name}`);
debug.textContent += `File: ${handle.name}\n`;
}
}
});