Human readable file size, extending Number type prototype

humanFileSize.js

Object.defineProperty(Number.prototype, 'fileSize', {
    value: function humanFileSize(si = false) {
        const divider = si ? 1e3 : 1024;
        const i = Math.floor(Math.log(this) / Math.log(divider));
        const fileSize =
            (this / Math.pow(divider, i)).toFixed(2) +
            ' ' + ['', 'k', 'M', 'G', 'T', 'P', 'E', 'Z', 'Y'][i] +
            (si ? 'i' : '');
        return fileSize.toString();
    },
    writable: false,
    enumerable: false
});