JSFiddle - React, Tailwind, and code Playground

HTML

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

JavaScript

function onfilechange(evt) {
    var selFile = evt.target.files[0];
    var reader = new FileReader();
    reader.onloadend = function (e) {
        console.log(e);
        console.log(new Int8Array(e.target.result));
    };
    reader.readAsArrayBuffer(selFile);
}
document.getElementById('file').addEventListener('change', onfilechange);