How to properly format file-size in JS

format_filesize.js

enum ByteFormatMode {
  Binary,   // 1024-based (KiB, MiB, GiB - IEC standard)
  Decimal,  // 1000-based (KB, MB, GB - SI standard)
  Pseudo    // 1024-based but uses KB/MB/GB (Windows-style)
}

function formatBytes(bytes: number, mode: ByteFormatMode = ByteFormatMode.Binary): string {
  const suffixesBinary = ["bytes", "KiB", "MiB", "GiB", "TiB", "PiB", "EiB", "ZiB", "YiB", "RiB", "QiB"];
  const suffixesDecimal = ["bytes", "KB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB", "RB", "QB"];
  const suffixesPseudo = ["bytes", "KB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB", "RB", "QB"];

  if (bytes === 0) return "0 bytes";
  if (bytes < 0) return `-${formatBytes(-bytes, mode)}`;

  const suffixes = (mode === ByteFormatMode.Decimal) ? suffixesDecimal : suffixesBinary;
  const unit = (mode === ByteFormatMode.Decimal) ? 1000 : 1024;

  const unitIndex = Math.floor(Math.log(bytes) / Math.log(unit));
  const safeUnitIndex = Math.min(unitIndex, suffixes.length - 1);
  const num = Math.round((bytes / Math.pow(unit, safeUnitIndex)) * 10) / 10;

  return `${num} ${suffixes[safeUnitIndex]}`;
}



/**
 * Formats bytes into a human-readable string with appropriate unit.
 * @param {number} bytes - The size in bytes.
 * @param {string} mode - "Binary" (IEC), "Decimal" (SI), or "Pseudo" (default: "Binary").
 * @returns {string} Formatted string with unit (e.g., "1.5 MiB").
 */
function formatBytes(bytes, mode = "Binary") {
    const suffixesBinary = ["bytes", "KiB", "MiB", "GiB", "TiB", "PiB", "EiB", "ZiB", "YiB", "RiB", "QiB"];
    const suffixesDecimal = ["bytes", "KB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB", "RB", "QB"];

    if (bytes === 0) return "0 bytes";
    if (bytes < 0) return "-" + formatBytes(-bytes, mode); // Handle negatives

    const suffixes = (mode === "Decimal") ? suffixesDecimal : suffixesBinary;
    const unit = (mode === "Decimal") ? 1000 : 1024;

    // Calculate the appropriate unit index (logarithmic scale)
    const unitIndex = Math.floor(Math.log(bytes) / Math.log(unit));
    const safeUnitIndex = Math.min(unitIndex, suffixes.length - 1); // Prevent overflow

    // Round to 1 decimal place
    const num = Math.round(bytes / Math.pow(unit, safeUnitIndex) * 10) / 10;

    return `${num} ${suffixes[safeUnitIndex]}`;
}


function formatInteger(number) {
    return number.toLocaleString('en-US').replace(/,/g, "'");
}

// Example usage:
console.log(formatInteger(1234567)); // Output: 1'234'567

function formatFloat(number, decimalPlaces = 2) {
    return number.toLocaleString('en-US', {
        minimumFractionDigits: decimalPlaces,
        maximumFractionDigits: decimalPlaces
    }).replace(/,/g, "'");
}

// Example usage:
console.log(formatFloat(1234567.89123)); // Output: 1'234'567.89
console.log(formatFloat(1234567.89123, 5)); // Output: 1'234'567.89123