Sending Files in JavaScript

Suppose you have an HTML element representing a button that lets users select a file. Upon clicking the button and choosing a file, its name is stored in document.getElementById("image-file").value. If the server supports multi-part POST requests at the URL "/upload/image," how do you send the file to that endpoint? Additionally, how do you monitor the upload's progress?

Pure JavaScript with Fetch

You can use the fetch API with optional await-try-catch handling:

let photo = document.getElementById("image-file").files[0];
let formData = new FormData();

formData.append("photo", photo);
fetch('/upload/image', {method: "POST", body: formData});

Example with Async-Try-Catch

This example also includes user data sent as JSON:

async function SavePhoto(inp) {
  let user = { name: 'john', age: 34 };
  let formData = new FormData();
  let photo = inp.files[0];

  formData.append("photo", photo);
  formData.append("user", JSON.stringify(user));

  const ctrl = new AbortController(); // for timeout
  setTimeout(() => ctrl.abort(), 5000);

  try {
    let r = await fetch('/upload/image', {
      method: "POST",
      body: formData,
      signal: ctrl.signal,
    });
    console.log('HTTP response code:', r.status);
  } catch (e) {
    console.log('Huston we have problem...:', e);
  }
}

Monitoring Upload Progress

Unfortunately, methods like request.onprogress are not supported in HTML5 file upload with fetch, but you can monitor the overall upload progress by listening to network events:

let xhr = new XMLHttpRequest();

xhr.upload.addEventListener('progress', function(e) {
  if (e.lengthComputable) {
    let percentComplete = (e.loaded / e.total) * 100;
    console.log('Upload progress:', percentComplete   '%');
  }
});

xhr.open('POST', '/upload/image');
xhr.send(formData);