// 创建一个新的FormData对象
const formData = new FormData();

// 添加文本数据
formData.append('username', 'JohnDoe');
formData.append('email', 'john@example.com');

// 添加文件数据
const fileInput = document.querySelector('input[type="file"]');
if (fileInput.files.length > 0) {
    formData.append('avatar', fileInput.files[0]);
}

// 添加JSON数据
const settings = { theme: 'dark', notifications: true };
formData.append('settings', JSON.stringify(settings));

// 使用XMLHttpRequest
const xhr = new XMLHttpRequest();
xhr.open('POST', '/api/upload');
xhr.onload = function() {
    if (xhr.status === 200) {
        console.log('上传成功', xhr.responseText);
    } else {
        console.error('上传失败');
    }
};
xhr.send(formData);

// 使用Fetch API
fetch('/api/upload', {
    method: 'POST',
    body: formData
})
.then(response => response.json())
.then(data => console.log('成功:', data))
.catch(error => console.error('错误:', error));

const express = require('express');
const multer = require('multer');
const upload = multer();

app.post('/api/upload', upload.none(), (req, res) => {
    console.log(req.body); // 包含表单数据
    res.send('数据接收成功');
});

const complexData = { user: { name: 'John', age: 30 } };
formData.append('userData', JSON.stringify(complexData));

xhr.upload.onprogress = function(event) {
    if (event.lengthComputable) {
        const percentComplete = (event.loaded / event.total) * 100;
        console.log(percentComplete + '% 已上传');
    }
};

const form = document.getElementById('myForm');
const formData = new FormData(form);

// 检查是否有特定键
formData.has('username'); // 返回true或false

// 获取特定键的值
formData.get('username'); // 返回第一个值

// 获取所有值
for (let [key, value] of formData.entries()) {
    console.log(key, value);
}

// 修改值（实际上是添加一个新值）
formData.set('username', 'NewUsername');

// 删除值
formData.delete('email');