fetch发起post/put请求
## 上传文件
```js
// 单个文件
function uploadSingleFile() {
const formData = new FormData();
const fileField = document.querySelector('input[type="file"]');
formData.append('username', 'abc123');
formData.append('avatar', fileField.files[0]);
fetch('https://example.com/profile/avatar', {
method: 'PUT',
body: formData,
})
.then((response) => response.json())
.then((result) => {
console.log('Success:', result);
})
.catch((error) => {
console.error('Error:', error);
});
}
// 多个文件
function uploadMultipleFiles() {
const formData = new FormData();
const photos = document.querySelector('input[type="file"][multiple]');
formData.append('title', 'title');
for (let i = 0; i < photos.files.length; i++) {
formData.append(`photos_${i}`, photos.files[i]);
}
fetch('https://example.com/posts', {
method: 'POST',
body: formData,
})
.then((response) => response.json())
.then((result) => {
console.log('Success:', result);
})
.catch((error) => {
console.error('Error:', error);
});
}
```
