Pressidian

Appearance

html
<!DOCTYPE html>
<html lang="zh-CN">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>FileReader文件读取最佳实践</title>
    <style>
        * {
            box-sizing: border-box;
            margin: 0;
            padding: 0;
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
        }

        body {
            background-color: darkorange;
            color: #333;
            min-height: 100vh;
            padding: 30px;
            display: flex;
            flex-direction: column;
            align-items: center;
        }

        .container {
            max-width: 1000px;
            width: 100%;
            background: rgba(255, 255, 255, 0.95);
            border-radius: 15px;
            box-shadow: 0 10px 40px rgba(0, 0, 0, 0.2);
            padding: 30px;
            margin-top: 20px;
            opacity: 0.95;
        }

        header {
            text-align: center;
            margin-bottom: 15px;
        }

        h1 {
            color: #2c3e50;
            font-size: 2.5rem;
            margin-bottom: 5px;
        }

        .subtitle {
            color: #7f8c8d;
            font-size: 1.2rem;
        }

        .upload-area {
            border: 3px dashed #3498db;
            border-radius: 12px;
            padding: 40px;
            text-align: center;
            margin: 25px 0;
            background: #f8f9fa;
            transition: all 0.3s;
            cursor: pointer;
        }

        .upload-area:hover {
            background: orange;
            border-color: red;
        }

        .upload-icon {
            font-size: 60px;
            color: #3498db;
            margin-bottom: 15px;
        }


        .file-input {
            display: none;
        }

        .btn {
            background: #3498db;
            color: white;
            border: none;
            padding: 12px 25px;
            border-radius: 6px;
            cursor: pointer;
            font-size: 1rem;
            font-weight: bold;
            transition: background 0.3s;
            margin: 10px 5px;
        }

        .btn:hover {
            background: pink;
        }

        .btn-secondary {
            background: #2ecc71;
        }

        .btn-secondary:hover {
            background: #1d9650;
        }

        .results {
            display: grid;
            grid-template-columns: 1fr 1fr;
            gap: 20px;
            margin-top: 30px;
        }

        .result-card {
            background: white;
            border-radius: 10px;
            box-shadow: 0 5px 15px rgba(0, 0, 0, 0.1);
            padding: 20px;
            overflow: hidden;
        }

        .result-card h3 {
            color: #3498db;
            margin-bottom: 15px;
            padding-bottom: 10px;
            border-bottom: 2px solid #f0f0f0;
        }

        .file-info {
            background: #e8f4fc;
            padding: 15px;
            border-radius: 8px;
            margin-bottom: 15px;
        }

        .preview {
            max-height: 300px;
            overflow: auto;
            padding: 15px;
            background: #f9f9f9;
            border-radius: 8px;
            border: 1px solid #eee;
            white-space: pre-wrap;
            font-family: 'Consolas', monospace;
        }

        .image-preview {
            max-width: 100%;
            max-height: 200px;
            display: block;
            margin: 0 auto;
            border-radius: 6px;
        }

        .progress-bar {
            height: 8px;
            background: #f0f0f0;
            border-radius: 4px;
            margin: 15px 0;
            overflow: hidden;
        }

        .progress {
            height: 100%;
            background: linear-gradient(90deg, #3498db, #2ecc71);
            width: 0%;
            transition: width 0.3s;
        }

        .status {
            text-align: center;
            padding: 10px;
            font-weight: bold;
            color: #7f8c8d;
        }

        .error {
            color: #e74c3c;
            padding: 15px;
            background: #fdecea;
            border-radius: 8px;
            margin: 15px 0;
        }

        @media (max-width: 768px) {
            .results {
                grid-template-columns: 1fr;
            }

            .container {
                padding: 20px;
            }

            h1 {
                font-size: 2rem;
            }
        }
    </style>
</head>

<body>
    <div class="container">
        <header>
            <h1>FileReader文件读取最佳实践</h1>
            <p class="subtitle">使用File API和FileReader读取本地文件内容</p>
        </header>

        <div class="upload-area" id="dropZone">
            <div class="upload-icon">📁</div>
            <h2>拖放文件到此处或点击选择文件</h2>
            <p>支持文本文件、图像、JSON等格式</p>
            <input type="file" id="fileInput" class="file-input" multiple>
            <button class="btn" onclick="document.getElementById('fileInput').click()">选择文件</button>
        </div>

        <div style="text-align: center;">
            <button class="btn btn-secondary" id="readAsTextBtn">读取为文本</button>
            <button class="btn btn-secondary" id="readAsDataURLBtn">读取为DataURL</button>
            <button class="btn btn-secondary" id="readAsArrayBufferBtn">读取为ArrayBuffer</button>
        </div>

        <div class="progress-bar">
            <div class="progress" id="progressBar"></div>
        </div>

        <div class="status" id="status">准备就绪</div>

        <div class="results">
            <div class="result-card">
                <h3>文件信息</h3>
                <div class="file-info" id="fileInfo">
                    <p>尚未选择文件</p>
                </div>
            </div>

            <div class="result-card">
                <h3>文件内容预览</h3>
                <div class="preview" id="filePreview">
                    <p>文件内容将显示在这里</p>
                </div>
            </div>
        </div>

        <div id="errorContainer"></div>
    </div>

    <script>
        // 获取文件的
        const fileInput = document.getElementById('fileInput');
        const dropZone = document.getElementById('dropZone');

        // 文件信息展示
        const fileInfo = document.getElementById('fileInfo');
        const filePreview = document.getElementById('filePreview');
        const progressBar = document.getElementById('progressBar');
        const status = document.getElementById('status');
        const errorContainer = document.getElementById('errorContainer');

        // 三个按钮
        const readAsTextBtn = document.getElementById('readAsTextBtn');
        const readAsDataURLBtn = document.getElementById('readAsDataURLBtn');
        const readAsArrayBufferBtn = document.getElementById('readAsArrayBufferBtn');

        // 当前选中的文件
        let currentFile = null;

        // 拖放功能
        dropZone.addEventListener('dragover', (e) => {
            e.preventDefault();
            dropZone.style.background = 'orange';
            dropZone.style.borderColor = 'red';

        });

        dropZone.addEventListener('dragleave', (e) => {
            e.preventDefault();
            dropZone.style.background = '#f8f9fa';
            dropZone.style.borderColor = '#3498db';
        });

        dropZone.addEventListener('drop', (e) => {
            e.preventDefault();
            dropZone.style.background = '#f8f9fa';
            dropZone.style.borderColor = '#3498db';


            console.log(e.dataTransfer);
            console.log(e);
            
            if (e.dataTransfer.files.length > 0) {
                handleFileSelection(e.dataTransfer.files[0]);
            }
        });

        // 文件选择处理
        fileInput.addEventListener('change', (e) => {
            if (e.target.files.length > 0) {
                handleFileSelection(e.target.files[0]);
            }
        });

        // 处理文件选择
        function handleFileSelection(file) {
            currentFile = file;
            console.log(file);
            console.log(typeof file);
            console.log(file instanceof File);
            // true 也就是说，在浏览器中读取的文件的类型就是File
            
            displayFileInfo(file);
            clearError();
            updateStatus('文件已选择，请选择读取方式');

            // 根据文件类型启用适当的按钮
            if (file.type.startsWith('image/')) {
                readAsDataURLBtn.disabled = false;
            } else {
                readAsDataURLBtn.disabled = false;
            }

            readAsTextBtn.disabled = false;
            readAsArrayBufferBtn.disabled = false;
        }

        // 显示文件信息
        function displayFileInfo(file) {
            fileInfo.innerHTML = `
                <p><strong>文件名:</strong> ${file.name}</p>
                <p><strong>类型:</strong> ${file.type || '未知'}</p>
                <p><strong>大小:</strong> ${formatFileSize(file.size)}</p>
                <p><strong>最后修改:</strong> ${new Date(file.lastModified).toLocaleString()}</p>
            `;
        }

        // 格式化文件大小
        function formatFileSize(bytes) {
            if (bytes === 0) return '0 Bytes';
            const k = 1024;
            const sizes = ['Bytes', 'KB', 'MB', 'GB'];
            const i = Math.floor(Math.log(bytes) / Math.log(k));
            return parseFloat((bytes / Math.pow(k, i)).toFixed(2)) + ' ' + sizes[i];
        }

        // 读取为文本
        readAsTextBtn.addEventListener('click', () => {
            if (!currentFile) {
                showError('请先选择文件');
                return;
            }

            const reader = new FileReader();

            reader.onloadstart = () => {
                updateStatus('开始读取文件...');
                progressBar.style.width = '30%';
            };

            reader.onprogress = (e) => {
                if (e.lengthComputable) {
                    const percentLoaded = Math.round((e.loaded / e.total) * 100);
                    progressBar.style.width = percentLoaded + '%';
                    updateStatus(`读取中: ${percentLoaded}%`);
                }
            };

            reader.onload = (e) => {
                progressBar.style.width = '100%';
                updateStatus('文件读取完成');

                // 显示文本内容
                filePreview.textContent = e.target.result;

                // 如果是JSON，尝试格式化
                if (currentFile.type === 'application/json' || currentFile.name.endsWith('.json')) {
                    try {
                        const json = JSON.parse(e.target.result);
                        filePreview.textContent = JSON.stringify(json, null, 2);
                    } catch (err) {
                        // 不是有效的JSON，保持原样
                    }
                }
            };

            reader.onerror = () => {
                showError('读取文件时发生错误: ' + reader.error.message);
                progressBar.style.width = '0%';
                updateStatus('读取失败');
            };

            reader.readAsText(currentFile);
        });

        // 读取为DataURL
        readAsDataURLBtn.addEventListener('click', () => {
            if (!currentFile) {
                showError('请先选择文件');
                return;
            }

            const reader = new FileReader();

            reader.onloadstart = () => {
                updateStatus('开始读取文件...');
                progressBar.style.width = '30%';
            };

            reader.onprogress = (e) => {
                if (e.lengthComputable) {
                    const percentLoaded = Math.round((e.loaded / e.total) * 100);
                    progressBar.style.width = percentLoaded + '%';
                    updateStatus(`读取中: ${percentLoaded}%`);
                }
            };

            reader.onload = (e) => {
                progressBar.style.width = '100%';
                updateStatus('文件读取完成');

                // 如果是图片，显示图片预览
                if (currentFile.type.startsWith('image/')) {
                    filePreview.innerHTML = `<img src="${e.target.result}" alt="预览" class="image-preview">`;
                } else {
                    // 否则显示DataURL的前100个字符
                    const dataURL = e.target.result;
                    filePreview.textContent = dataURL.substring(0, 100) + '...';
                }
            };

            reader.onerror = () => {
                showError('读取文件时发生错误: ' + reader.error.message);
                progressBar.style.width = '0%';
                updateStatus('读取失败');
            };

            reader.readAsDataURL(currentFile);
        });

        // 读取为ArrayBuffer
        readAsArrayBufferBtn.addEventListener('click', () => {
            if (!currentFile) {
                showError('请先选择文件');
                return;
            }

            const reader = new FileReader();

            reader.onloadstart = () => {
                updateStatus('开始读取文件...');
                progressBar.style.width = '30%';
            };

            reader.onprogress = (e) => {
                if (e.lengthComputable) {
                    const percentLoaded = Math.round((e.loaded / e.total) * 100);
                    progressBar.style.width = percentLoaded + '%';
                    updateStatus(`读取中: ${percentLoaded}%`);
                }
            };

            reader.onload = (e) => {
                progressBar.style.width = '100%';
                updateStatus('文件读取完成');

                // 显示ArrayBuffer信息
                const arrayBuffer = e.target.result;
                filePreview.innerHTML = `
                    <p><strong>ArrayBuffer大小:</strong> ${arrayBuffer.byteLength} 字节</p>
                    <p><strong>前16字节:</strong> ${getFirstBytes(arrayBuffer, 16)}</p>
                `;
            };

            reader.onerror = () => {
                showError('读取文件时发生错误: ' + reader.error.message);
                progressBar.style.width = '0%';
                updateStatus('读取失败');
            };

            reader.readAsArrayBuffer(currentFile);
        });

        // 获取ArrayBuffer的前几个字节
        function getFirstBytes(arrayBuffer, count) {
            const uint8Array = new Uint8Array(arrayBuffer);
            const bytes = [];
            for (let i = 0; i < Math.min(count, uint8Array.length); i++) {
                bytes.push(uint8Array[i].toString(16).padStart(2, '0'));
            }
            return bytes.join(' ');
        }

        // 更新状态
        function updateStatus(message) {
            status.textContent = message;
        }

        // 显示错误
        function showError(message) {
            errorContainer.innerHTML = `<div class="error">${message}</div>`;
        }

        // 清除错误
        function clearError() {
            errorContainer.innerHTML = '';
        }

        // 初始化按钮状态
        readAsTextBtn.disabled = true;
        readAsDataURLBtn.disabled = true;
        readAsArrayBufferBtn.disabled = true;
    </script>
</body>

</html>