js实现文件功能

<input type="file" id="fileInput">
<script>
document.getElementById('fileInput').addEventListener('change', function(event) {
    let file = event.target.files[0];
    if (file) {
        let reader = new FileReader();
        reader.onload = function(e) {
            console.log(e.target.result); // 文件内容
        };
        reader.readAsText(file);
    }
});
</script>

<form id="uploadForm">
    <input type="file" name="file">
    <button type="submit">上传</button>
</form>
<script>
document.getElementById('uploadForm').addEventListener('submit', function(event) {
    event.preventDefault();
    let formData = new FormData(this);
    fetch('/upload', {
        method: 'POST',
        body: formData
    }).then(response => response.json())
      .then(data => console.log(data));
});
</script>

function downloadFile(content, filename, contentType) {
    let blob = new Blob([content], { type: contentType });
    let url = URL.createObjectURL(blob);
    let a = document.createElement('a');
    a.href = url;
    a.download = filename;
    document.body.appendChild(a);
    a.click();
    document.body.removeChild(a);
    URL.revokeObjectURL(url);
}

// 使用示例
let csvContent = "data:text/csv;charset=utf-8,Name,Age\nJohn,30\nJane,28";
downloadFile(csvContent, 'data.csv', 'text/csv');

let xhr = new XMLHttpRequest();
xhr.upload.onprogress = function(event) {
    if (event.lengthComputable) {
        let percentComplete = (event.loaded / event.total) * 100;
        console.log(percentComplete + '% uploaded');
    }
};
xhr.open('POST', '/upload');
xhr.send(formData);