@prexjs/etag

Generate HTTP ETags from strings, Buffers, and fs.Stats objects.

@prexjs/etag generates HTTP entity tags (ETags) for web servers and caching layers. It supports strong and weak entity tags and integrates directly with Node.js fs.Stats objects for ultra-fast static file caching without reading file bodies.

Features

• Generates strong ETags from strings and Buffers using SHA-1 digest + byte length.
• Generates weak ETags directly from fs.Stats (mtime and size) without reading disk contents.
• Fast-path for empty bodies.
• Dual ES Module (.mjs) and CommonJS (.cjs) support with TypeScript definitions.
• Zero external runtime dependencies.

Installation

Install using your preferred package manager:

# npm
npm install @prexjs/etag

# pnpm
pnpm add @prexjs/etag

# Yarn
yarn add @prexjs/etag

# Bun
bun add @prexjs/etag

Quick start

import etag from '@prexjs/etag';
import http from 'node:http';

const server = http.createServer((req, res) => {
  const body = 'Hello World';
  const tag = etag(body);

  if (req.headers['if-none-match'] === tag) {
    res.statusCode = 304;
    res.end();
    return;
  }

  res.setHeader('ETag', tag);
  res.end(body);
});

Both default and named exports are supported:

import etag, { etag as namedEtag, type EtagOptions } from '@prexjs/etag';

Examples

Generating strong and weak tags

import etag from '@prexjs/etag';

// Strong ETag for string
console.log(etag('hello'));
// '"5-qvTGHdzF6KLavt4PO0gs2a6pQ00"'

// Force weak ETag
console.log(etag('hello', { weak: true }));
// 'W/"5-qvTGHdzF6KLavt4PO0gs2a6pQ00"'

Static file stats caching

import fs from 'node:fs';
import etag from '@prexjs/etag';

fs.stat('package.json', (err, stats) => {
  if (err) return;
  // Automatically creates weak ETag based on mtime and size
  const tag = etag(stats);
  console.log(tag); // 'W/"..."'
});

Compatibility

@prexjs/etag is designed for JavaScript and TypeScript projects running on Node.js, Deno, or Bun with node:crypto and node:fs support.

License

This project is licensed under the MIT License. See LICENSE for the full license text.

Related projects

• prex.js — prex.js monorepo and ecosystem.