SOURCE

function change(e) {
    const files = e.target.files;
    console.log(files)
    const formData = new FormData()
    for(let i = 0;i<files.length;i++){
        const file = files[i]
        formData.append('files', file, file.name)
    }
    let request = new XMLHttpRequest();
    request.open("POST", "https://jsonplaceholder.typicode.com/posts/");
    request.send(formData);
}
const input = document.getElementById('input')
input.onchange = change

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