JSFiddle - React, Tailwind, and code Playground

HTML

<input type="file" id="file"/>

JavaScript

document.getElementById('file').addEventListener('change', function(e) {
    var file = this.files[0];
    var formData = new FormData();    
    formData.append('thefile', file);
    
    var xhr = new XMLHttpRequest();    
    xhr.onreadystatechange = function(e) {
        if (this.readyState === 4) {
            alert('Uploaded!');
        }
    }

    xhr.open('post', '/echo/json/', true);
    xhr.setRequestHeader('Content-Type', 'multipart/form-data');
    xhr.send(formData);
}, false);