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Upload files with Ajax

Written byPhuoc Nguyen
Level 1 — Basic
17 Mar, 2020
Last updated
03 Apr, 2020
The function below sends selected files from a `fileEle` element to a back-end:
const upload = function (fileEle, backendUrl) {
return new Promise(function (resolve, reject) {
// Get the list of selected files
const files = fileEle.files;

// Create a new FormData
const formData = new FormData();

// Loop over the files
[].forEach.call(files, function (file) {
formData.append(fileEle.name, file, file.name);

// Create new Ajax request
const req = new XMLHttpRequest();
req.open('POST', backendUrl, true);

// Handle the events
req.onload = function () {
if (req.status >= 200 && req.status < 400) {
req.onerror = function () {

// Send it


Assume that we have a `file` input that allows user to choose multiple files:
<input type="file" id="upload" multiple />
We can use the following code inside a `click` event handler of a button which performs the uploading:
const fileEle = document.getElementById('upload');

upload(fileEle, '/path/to/back-end').then(function(response) {
// `response` is what we got from the back-end
// We can parse it if the server returns a JSON
const data = JSON.parse(response);

See also

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Phước Nguyễn