human-readable file size in JavaScript (made with https://codeeval.dev)

filesize.js

// https://raw.githubusercontent.com/avoidwork/filesize.js/master/src/filesize.js
/**
	 * filesize
	 *
	 * @method filesize
	 * @param  {Mixed}   arg        String, Int or Float to transform
	 * @param  {Object}  descriptor [Optional] Flags
	 * @return {String}             Readable file size String
	 */
function filesize (arg, descriptor = {}) {
    let result = [],
        val = 0,
        e, base, bits, ceil, full, fullforms, locale, localeOptions, neg, num, output, round, unix, separator, spacer, standard, symbols;

    if (isNaN(arg)) {
        throw new TypeError("Invalid number");
    }

    bits = descriptor.bits === true;
    unix = descriptor.unix === true;
    base = descriptor.base || 2;
    round = descriptor.round !== void 0 ? descriptor.round : unix ? 1 : 2;
    locale = descriptor.locale !== void 0 ? descriptor.locale : "";
    localeOptions = descriptor.localeOptions || {};
    separator = descriptor.separator !== void 0 ? descriptor.separator : "";
    spacer = descriptor.spacer !== void 0 ? descriptor.spacer : unix ? "" : " ";
    symbols = descriptor.symbols || {};
    standard = base === 2 ? descriptor.standard || "jedec" : "jedec";
    output = descriptor.output || "string";
    full = descriptor.fullform === true;
    fullforms = descriptor.fullforms instanceof Array ? descriptor.fullforms : [];
    e = descriptor.exponent !== void 0 ? descriptor.exponent : -1;
    num = Number(arg);
    neg = num < 0;
    ceil = base > 2 ? 1000 : 1024;

    // Flipping a negative number to determine the size
    if (neg) {
        num = -num;
    }

    // Determining the exponent
    if (e === -1 || isNaN(e)) {
        e = Math.floor(Math.log(num) / Math.log(ceil));

        if (e < 0) {
            e = 0;
        }
    }

    // Exceeding supported length, time to reduce & multiply
    if (e > 8) {
        e = 8;
    }

    if (output === "exponent") {
        return e;
    }

    // Zero is now a special case because bytes divide by 1
    if (num === 0) {
        result[0] = 0;
        result[1] = unix ? "" : symbol[standard][bits ? "bits" : "bytes"][e];
    } else {
        val = num / (base === 2 ? Math.pow(2, e * 10) : Math.pow(1000, e));

        if (bits) {
            val = val * 8;

            if (val >= ceil && e < 8) {
                val = val / ceil;
                e++;
            }
        }

        result[0] = Number(val.toFixed(e > 0 ? round : 0));

        if (result[0] === ceil && e < 8 && descriptor.exponent === void 0) {
            result[0] = 1;
            e++;
        }

        result[1] = base === 10 && e === 1 ? bits ? "kb" : "kB" : symbol[standard][bits ? "bits" : "bytes"][e];

        if (unix) {
            result[1] = standard === "jedec" ? result[1].charAt(0) : e > 0 ? result[1].replace(/B$/, "") : result[1];

            if (b.test(result[1])) {
                result[0] = Math.floor(result[0]);
                result[1] = "";
            }
        }
    }

    // Decorating a 'diff'
    if (neg) {
        result[0] = -result[0];
    }

    // Applying custom symbol
    result[1] = symbols[result[1]] || result[1];

    if (locale === true) {
        result[0] = result[0].toLocaleString();
    } else if (locale.length > 0) {
        result[0] = result[0].toLocaleString(locale, localeOptions);
    } else if (separator.length > 0) {
        result[0] = result[0].toString().replace(".", separator);
    }

    // Returning Array, Object, or String (default)
    if (output === "array") {
        return result;
    }

    if (full) {
        result[1] = fullforms[e] ? fullforms[e] : fullform[standard][e] + (bits ? "bit" : "byte") + (result[0] === 1 ? "" : "s");
    }

    if (output === "object") {
        return {value: result[0], symbol: result[1]};
    }

    return result.join(spacer);
}

// Partial application for functional programming
filesize.partial = opt => arg => filesize(arg, opt);