js检查文件类型

<input type="file" id="fileInput" />

document.getElementById('fileInput').addEventListener('change', function(event) {
    const file = event.target.files[0];
    if (file) {
        console.log('MIME Type:', file.type);
    }
});

function getFileType(arrayBuffer) {
    const bytes = new Uint8Array(arrayBuffer);
    if (bytes[0] === 0xFF && bytes[1] === 0xD8) {
        return 'image/jpeg';
    } else if (bytes[0] === 0x89 && bytes[1] === 0x50 && bytes[2] === 0x4E && bytes[3] === 0x47) {
        return 'image/png';
    }
    // 其他类型的检查...
    return 'application/octet-stream';
}

document.getElementById('fileInput').addEventListener('change', function(event) {
    const file = event.target.files[0];
    if (file) {
        const reader = new FileReader();
        reader.onloadend = function() {
            const fileType = getFileType(reader.result);
            console.log('Detected File Type:', fileType);
        };
        reader.readAsArrayBuffer(file);
    }
});

function getFileExtension(filename) {
    return filename.slice((filename.lastIndexOf(".") - 1 >>> 0) + 2).toLowerCase();
}

document.getElementById('fileInput').addEventListener('change', function(event) {
    const file = event.target.files[0];
    if (file) {
        const extension = getFileExtension(file.name);
        console.log('File Extension:', extension);
    }
});