node-md5

md5 is a single-purpose JavaScript library that hashes messages using the MD5 algorithm. It accepts strings, Node.js Buffers, arrays, and Uint8Array instances, and returns a hex digest by default (with options for raw bytes or a binary string). The implementation is a pure-JavaScript port of the classic MD5 algorithm originally published by Ronald Rivest in 1991, adapted from Jeff Mott’s CryptoJS implementation.

Because it has no native bindings and only a handful of small dependencies (crypt, charenc, is-buffer), it works identically in Node.js and in the browser (via bundlers like webpack). It has shipped as the md5 npm package since 2011 and is widely used as a drop-in hashing utility for cache keys, checksums, Gravatar URLs, and other non-cryptographic identity-hashing use cases.

What You Get

• A single md5(message, options) function that returns a 32-character hex digest by default
• Support for hashing strings, Node.js Buffers, plain arrays, and Uint8Array instances
• An asBytes option to get the raw digest as a byte array instead of a hex string
• An asString option to get the digest as a binary string, plus an encoding: 'binary' option for binary-encoded string input
• Isomorphic support for both Node.js and browser bundles (webpack config included in the repo)

Common Use Cases

• Generating Gravatar avatar URLs from a hashed email address
• Producing cache keys or checksums for request/response deduplication
• Computing quick file or content fingerprints where cryptographic strength isn’t required
• Hashing form or upload data client-side before sending it to an API
• Providing a lightweight MD5 fallback in environments without Node’s built-in crypto module (e.g. certain browser bundles)

Under The Hood

Architecture

The library is a single self-contained module (md5.js) wrapped in an IIFE that exports one function. Internally it delegates byte/word conversion to the sibling crypt package and string-encoding handling to charenc, while is-buffer detects Node.js Buffers so the same code path can normalize strings, buffers, arrays, and typed arrays before running the standard MD5 compression rounds (_ff/_gg/_hh/_ii). There is no class hierarchy or plugin surface — all branching for input type and output format happens inline in the exported wrapper, making the whole library effectively one function plus its four auxiliary round functions.

Tech Stack

Plain, untyped JavaScript with no build step for the library itself — md5.js is shipped directly as the package’s main entry. It depends on three small same-author-adjacent helper packages (crypt, charenc, is-buffer) rather than a general-purpose crypto framework. Mocha is used for tests and webpack is configured (via webpack.config.js) purely to produce a browser bundle for the demo page, not as part of the published package.

Code Quality

test.js runs a small mocha/assert suite covering known hash vectors, Buffer and Uint8Array input, encoding options, and error-throwing on null/undefined input — a reasonable but limited set of cases for a single-function library. There are no TypeScript types, no linter configuration, and no active CI workflow (the README’s Travis badge points at a service the project no longer effectively uses); naming and error handling are simple and consistent throughout the small codebase.

API Design The public surface is intentionally tiny: one function, one options object with three well-documented flags (asBytes, asString, encoding). This minimizes onboarding friction — there is effectively nothing to configure — at the cost of no support for streaming large inputs or incremental hashing, which some hashing libraries offer.