Generate a hash mapping for your assets, to burst cache


Generate a hash mapping for your assets files, in order to burst cache

This plugin requires Grunt ~0.4.0

If you haven't used Grunt before, be sure to check out the Getting Started guide, as it explains how to create a Gruntfile as well as install and use Grunt plugins. Once you're familiar with that process, you may install this plugin with this command:

npm install grunt-hashmap --save-dev

One the plugin has been installed, it may be enabled inside your Gruntfile with this line of JavaScript:


In your project's Gruntfile, add a section named hashmap to the data object passed into grunt.initConfig().

  hashmap: {
    options: {
      // These are default options 
      output: '#{= dest}/hash.json',
      etag: null, // See below([#](#option-etag)) 
      algorithm: 'md5', // the algorithm to create the hash 
      rename: '#{= dirname}/#{= basename}_#{= hash}#{= extname}', // save the original file as what 
      keep: true, // should we keep the original file or not 
      merge: false, // merge hash results into existing `hash.json` file or override it. 
      hashlen: 10, // length for hashsum digest 
    your_target: {
      // Target-specific file lists and/or options go here. 
      options: {
        output: 'static/versions.json',
      files: {
        cwd: 'static/dist',
        src: ['js/**/*.js', 'css/**/*.css'],
        dest: 'static/dist'

In your express application, add a static_url generator to template helpers:

var path = require('path');
var hash_cache = require('./static/hash.json');
var reg_css_js = /\.(css|js)$/;
// change these consts according to the app's running environment 
var STATIC_ROOT = '';
var DEBUG = false;
function static_url(p) {
  if (p[0] == '/') p = p.slice(1);
  if (DEBUG || !reg_css_js.test(p)) return STATIC_ROOT + '/' + p;
  var hash = hash_cache[p];
  if (hash) {
    var ext = path.extname(p);
    p = path.join(path.dirname(p), path.basename(p, ext) + '_' + hash + ext); 
  return STATIC_ROOT + '/' + p;
  static: static_url

In your template, always refer to static file url like this:


The output would be:

<script type="text/javascript" src=""></script>
<!-- or when in debug mode: -->
<script type="text/javascript" src="/css/abc.css"></script>

Type: String Default value: '#{= dest}/hash.json'

Where to save the hash mapping json file. Available variables are dest, cwd. You can always use #{= grunt.config.get(...) }' to access config data in your Gruntfile.

Set to null will disable the output.

The output format:

  "a/b.js": "aaa93n3f2",
  "foo.css": "maaof33mao"


Type: String Default value: null

In spite of standard digest algorithms provided by the crypto module, you can set a "etag" format to use as file version.

Set etag to true will use the default format: #{= size}-#{= +mtime}.

All values in a fs.Stats result are available.

Type: String Default value: 'md5'

The algorithm to generate hash digests. Depend on the version of OpenSSL on the platform. Examples are 'sha1', 'md5', 'sha256', etc.

Type: Number Default value: 10

The length of a hash digest hex value.

Type: String Default value: '#{= dirname}/#{= basename}\_#{= hash}#{= extname}'

Rename files, to include a hash in it. This is often for safely bursting cache. Available variables are:

  • hash - The hash/etag value.
  • dest - The destination directory.
  • cwd - The cwd you setted for files prop section.
  • filepath - The path of the file.
  • basename - The basename of the file, with extension name excluded.
  • dirname - The directory name of the file.
  • extname - The extension name of the file.


"abc/defg/hijk.js" =>
  filepath: "abc/defg/hijk.js",
  basename: "hijk",
  dirname: "abc/defg",
  extname: "js"

With the default rename format, the result will be something like "abc/defg/hijk\_e8e7f9e4.js".

Will raise a warning if the renamed target is not in dest directory.

Type: String Default value: true

Whether to keep the original files after rename it.

Type: String Default value: false

This option is mainly for cases like this:

  hashmap: {
    options: {
      output: 'static/hash.json',
      merge: true,
    js: {
      cwd: 'static/dist',
      src: 'js/**/*.js',
      dest: 'static/dist'
    css: {
      cwd: 'static/dist',
      src: 'css/**/*.css',
      dest: 'static/dist'
  watch: {
    js: {
      files: ['static/js/**/*.js'],
      tasks: ['hashmap:js']
    css: {
      files: ['static/css/**/*.css'],
      tasks: ['hashmap:css']

Hashmap tasks for css and js are created seperately. So with the grunt-contrib-watch running, when you modify one single file, grunt won't need to run the whole hash mapping process for all files.

Since all the hash results will be written to the same file, and the hashmaps are automatically merged. It is safe to refer to hash.json for all static files in your application's static url generator.

The downside of this practice is that hashes for deleted files will never be removed, unless hash.json is removed. But of course, you can always set up a grunt clean task.

In lieu of a formal styleguide, take care to maintain the existing coding style. Add unit tests for any new or changed functionality. Lint and test your code using Grunt.

  • 0.1.5 - add option.salt to burst all the cache, thanks @theoephraim
  • 0.1.4 - format output json, and sort it by filenames (diff a hashmap made easy). Thanks @dpolivy !
  • 0.1.1 - add options.encoding for file contents reading
  • 0.1.0 - first release