How do I upload a file with the JS fetch API?

问题

I am still trying to wrap my head around it.

I can have the user select the file (or even multiple) with the file input:

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

And I can catch the submit event using <fill in your event handler here>. But once I do, how do I send the file using fetch?

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

回答1:

This is a basic example with comments. The upload function is what you are looking for:

// 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);

回答2:

I've done it like this:

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
})

回答3:

An important note for sending Files with Fetch API

One needs to omit content-type header for the Fetch request. Then the browser will automatically add the Content type header including the Form Boundary which looks like

Content-Type: multipart/form-data; boundary=—-WebKitFormBoundaryfgtsKTYLsT7PNUVD

Form boundary is the delimiter for the form data

回答4:

If you want multiple files, you can use this

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

var data = new FormData()
for (const file of input.files) {
  data.append('files',file,file.name)
}

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

回答5:

To submit a single file, you can simply use the File object from the input's .files array directly as the value of body: in your fetch() initializer:

const myInput = document.getElementById('my-input');

// Later, perhaps in a form 'submit' handler or the input's 'change' handler:
fetch('https://example.com/some_endpoint', {
  method: 'POST',
  body: myInput.files[0],
});

This works because File inherits from Blob, and Blob is one of the permissible BodyInit types defined in the Fetch Standard.

回答6:

Jumping off from Alex Montoya's approach for multiple file input elements

const inputFiles = document.querySelectorAll('input[type="file"]');
const formData = new FormData();

for (const file of inputFiles) {
    formData.append(file.name, file.files[0]);
}

fetch(url, {
    method: 'POST',
    body: formData })

回答7:

The problem for me was that I was using a response.blob() to populate the form data. Apparently you can't do that at least with react native so I ended up using

data.append('fileData', {
  uri : pickerResponse.uri,
  type: pickerResponse.type,
  name: pickerResponse.fileName
 });

Fetch seems to recognize that format and send the file where the uri is pointing.

来源：https://stackoverflow.com/questions/36067767/how-do-i-upload-a-file-with-the-js-fetch-api

标签

javascript

fetch-api