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

user_736714 0
Viewed 316265

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 */);
fetch-api javascript
11 Answers

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
})
user_96558390

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.

user_17095870

The accepted answer here is a bit dated. As of April 2020, a recommended approach seen on the MDN website suggests using FormData and also does not ask to set the content type. https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch

I'm quoting the code snippet for convenience:

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);
});
user_12996690

It would be nice to add php endpoint example. So that is js:

const uploadinput = document.querySelector('#uploadinputid');
const uploadBtn = document.querySelector('#uploadBtnid');
uploadBtn.addEventListener('click',uploadFile);

async function uploadFile(){
    const formData = new FormData();
    formData.append('nameusedinFormData',uploadinput.files[0]);    
    try{
        const response = await fetch('server.php',{
            method:'POST',
            body:formData
        } );
        const result = await response.json();
        console.log(result);
    }catch(e){
        console.log(e);

    }
}

That is php:

$file = $_FILES['nameusedinFormData'];
$temp = $file['tmp_name'];
$target_file = './targetfilename.jpg';
move_uploaded_file($_FILES["image"]["tmp_name"], $target_file);
user_89661570

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 })
user_94033930

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.

user_10290300

Here is my code:

html: 

const upload = (file) => {
    console.log(file);

    

    fetch('http://localhost:8080/files/uploadFile', { 
    method: 'POST',
    // headers: {
    //   //"Content-Disposition": "attachment; name='file'; filename='xml2.txt'",
    //   "Content-Type": "multipart/form-data; boundary=BbC04y " //"multipart/mixed;boundary=gc0p4Jq0M2Yt08jU534c0p" //  ή // multipart/form-data 
    // },
    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
  );

  //cvForm.submit();
};

const onSelectFile = () => upload(uploadCvInput.files[0]);

uploadCvInput.addEventListener('change', onSelectFile, false);
<form id="cv_form" style="display: none;"
          enctype="multipart/form-data">
          <input id="uploadCV" type="file" name="file"/>
          <button type="submit" id="upload_btn">upload</button>
</form>
<ul class="dropdown-menu">
<li class="nav-item"><a class="nav-link" href="#" id="upload">UPLOAD CV</a></li>
<li class="nav-item"><a class="nav-link" href="#" id="download">DOWNLOAD CV</a></li>
</ul>

user_125303900

How to upload a single file on select using HTML5 fetch

<label role="button">
  Upload a picture
  <input accept="image/*" type="file" hidden />
</label>

const input = document.querySelector(`input[type="file"]`);

function upload() {
  fetch(uplaodURL, { method: "PUT", body: input.files[0] });
}

input.addEventListener("change", upload);
user_826860
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