如何使用 JS fetch API 上传文件？

Question

我仍然试图绕过它。

我可以让用户使用文件输入选择文件（甚至多个）：

<form>
  <div>
    <label>Select file to upload</label>
    <input type="file">
  </div>
  <button type="submit">Convert</button>
</form>

我可以使用 submit 来捕获 <fill in your event handler here> 事件。但是一旦我这样做了，如何使用 fetch 发送文件？

fetch('/files', {
  method: 'post',
  // what goes here? What is the "body" for this? content-type header?
}).then(/* whatever */);

原文由 deitch 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 1

这是一个带有注释的基本示例。 upload 功能就是你要找的：

 // Select your input type file and store it in a variable
 const input = document.getElementById('fileinput');

 // This will upload the file after having read it
 const upload = (file) => {
 fetch('http://www.example.net', { // Your POST endpoint
 method: 'POST',
 headers: {
 // Content-Type may need to be completely **omitted**
 // or you may need something
 "Content-Type": "You will perhaps need to define a content-type here"
 },
 body: file // This is your file object
 }).then(
 response => response.json() // if the response is a JSON object
 ).then(
 success => console.log(success) // Handle the success response object
 ).catch(
 error => console.log(error) // Handle the error response object
 );
 };

 // Event handler executed when a file is selected
 const onSelectFile = () => upload(input.files[0]);

 // Add a listener on your input
 // It will be triggered when a file will be selected
 input.addEventListener('change', onSelectFile, false);

原文由 Damien 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 2

我是这样做的：

 var input = document.querySelector('input[type="file"]')

var data = new FormData()
data.append('file', input.files[0])
data.append('user', 'hubot')

fetch('/avatars', {
  method: 'POST',
  body: data
})

原文由 Integ 发布，翻译遵循 CC BY-SA 3.0 许可协议