ReadTextFile.html

<input type="file" id="fs" multiple> <br>
<small id="target"></small>

ReadTextFile.js

// Prepare a function to decode base 64 unicode
function b64DecodeUnicode(str) {
    return decodeURIComponent(Array.prototype.map.call(atob(str), function (c) {
        return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2);
    }).join(''));
}
// Create file reader Event Listener
const reader = new FileReader();
reader.addEventListener('load', (event) => {
    eventdata = event.target;
    const result_base_64 = event.target.result;
    const result_decoded = b64DecodeUnicode(result_base_64.split(',')[1]);
    console.log(result_decoded);
    document.getElementById("target").innerHTML = result_decoded;
});

// Event Listener for file input
const fileSelect = document.getElementById('fs');
fileSelect.addEventListener('change', (event) => {
    const fileList = event.target.files;
    for (const file of fileList) {
        console.log("read file");
        reader.readAsDataURL(file);
    }
})