JavaScript To Convert Bytes To MB, KB, Etc

bytesToSize.js

// from http://scratch99.com/web-development/javascript/convert-bytes-to-mb-kb/
function bytesToSize(bytes) {
    var sizes = ['Bytes', 'KB', 'MB', 'GB', 'TB'];
    if (bytes == 0) return 'n/a';
    var i = parseInt(Math.floor(Math.log(bytes) / Math.log(1024)));
    if (i == 0) return bytes + ' ' + sizes[i];
    return (bytes / Math.pow(1024, i)).toFixed(1) + ' ' + sizes[i];
};

@HaukeHa Thank you for noticing 👍 

I use the following code:

export function convertBytes(bytes: number, options: { useBinaryUnits?: boolean; decimals?: number } = {}): string {
  const { useBinaryUnits = false, decimals = 2 } = options;

  if (decimals < 0) {
    throw new Error(`Invalid decimals ${decimals}`);
  }

  const base = useBinaryUnits ? 1024 : 1000;
  const units = useBinaryUnits
    ? ["Bytes", "KiB", "MiB", "GiB", "TiB", "PiB", "EiB", "ZiB", "YiB"]
    : ["Bytes", "KB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB"];

  const i = Math.floor(Math.log(bytes) / Math.log(base));

  return `${(bytes / Math.pow(base, i)).toFixed(decimals)} ${units[i]}`;
}

and basic tests:

import { describe, expect } from "vitest";
import { convertBytes } from "./bytes";

describe("convertBytes", () => {
  const fileSizeInBytes = 2048;

  describe("default conversion", () => {
    it("should convert to KB", () => {
      const resultKB = convertBytes(fileSizeInBytes);
      expect(resultKB).toBe("2.05 KB");
    });

    it("should convert to MB", () => {
      const resultMB = convertBytes(fileSizeInBytes * 1000);
      expect(resultMB).toBe("2.05 MB");
    });

    it("should throw an error for invalid decimals", () => {
      expect(() => convertBytes(fileSizeInBytes, { decimals: -1 })).toThrowError("Invalid decimals -1");
    });
  });

  describe("conversion to binary units", () => {
    it("should convert to KiB", () => {
      const resultKiB = convertBytes(fileSizeInBytes, { useBinaryUnits: true });
      expect(resultKiB).toBe("2.00 KiB");
    });

    it("should convert to MiB", () => {
      const resultMiB = convertBytes(fileSizeInBytes * 1024, { useBinaryUnits: true });
      expect(resultMiB).toBe("2.00 MiB");
    });
  });

  it("should handle very large bytes (Number.MAX_SAFE_INTEGER)", () => {
    const result = convertBytes(Number.MAX_SAFE_INTEGER);
    expect(result).toBe("9.01 PB");
  });
});

  const units = ["byte", "kilobyte", "megabyte", "terabyte", "petabyte"];

you lost "gigabyte"