node package manager


Static asset manager for Node.JS and Express


node-static-asset is a static asset manager for Node.JS, designed for Express. This project aims to solve the problem of caching static assets (including assets like *.js files that might change from time to time).


Google has a nice article about "strong" and "weak" caching. It's worth a quick read if you don't know what that means.


npm install static-asset

Getting Started

node-static-asset allows you to generate URL fingerprints for static assets.

  1. Add the static-asset middleware to your Express stack
var staticAsset = require('static-asset');
app.use(staticAsset(__dirname + "/public/") );
  1. Get URL fingerprints of your static resources using req.assetFingerprint or the assetFingerprint view helper function.
app.get("/info", function(req, res, next) {
    /* Should return something like "The URL fingerprint for jQuery is:
    res.type("text/plain").send("The URL fingerprint for jQuery is: " +
        req.assetFingerprint("/js/jquery.min.js") );

Now that you have obtained the asset fingerprint for /js/jquery.min.js, if you send a request for that asset to the URL /js/jquery.min.js?v=3dd-983jk2a, static-asset will automatically add appropriate caching headers (i.e. Last-Modified, ETag, and Expires).


static-asset exposes a function req.assetFingerprint, which allows one to generate and register URL fingerprints for static assets.

Once a URL fingerprint is registered with static-asset, any HTTP request for that static asset (i.e. when req.url matches the registered URL fingerprint) will trigger static-asset to set certain HTTP headers (i.e. Last-Modified, ETag, or Expires).

Adding the middleware function

require('static-asset')(path[, cache]) - Returns an Express middleware function that exposes a req.assetFingerprint function and adds assetFingerprint view helper function to res.locals. If any request's URL matches a previously generated URL fingerprint, static-asset will attempt to add weak and strong caching headers to the HTTP response.

  • path - the path from which static files are served
  • cache - a "cache strategy" Object, which must implement all "cache strategy" methods, as described below. If cache is omitted, the default "cache stategy" is used.

A "Cache Strategy" Object

A "cache strategy" object should implement one or more of the following methods:

  • lastModified(filename) - a function that accepts a filename and returns its last modified date. If a last modified date could not be determined, the function should return null; otherwise, static-asset may use this Date to set the Last-Modified HTTP response header when the resource is requested.
  • etag(filename, cb) - Same as lastModified (above), except that it must return an ETag (or hash value). If the returned ETag is not null, static-asset may use this value to set the ETag HTTP header when the named resource is requested.
  • expires(filename) - Same as lastModified (above), except that it must return a Date Object indicating when the resource shall expire. The Date may be no more than one year in the future. If expires is implemented, static-asset may use the date to set an Expires and/or Cache-Control: max-age HTTP headers; otherwise, static-asset will use a Date approximately one year into the future.
  • fileFingerprint(filename, fullPath) - Returns the URL fingerprint of the resource filename, stored at the location fullPath. fullPath is provided for convenience, since the caching strategy does not know what root path was passed into the static-asset middleware.

Registering URL fingerprints

req.assetFingerprint(label_or_filename) - Return a URL fingerprint for the labelled resource, or if no such label is registered, use the "cache strategy" to determine the file's ETag or last modified date. If you're confused by this description, read on...

If you call req.assetFingerprint(filename) and pass a filename relative to the path from which static files are served, static-asset will use the cache strategy you specified to generate and return a unique URL fingerprint for the asset. If that file is requested later by the URL fingerprint, static-asset will respond by setting the appropriate HTTP headers like Last-Modified, ETag, and Expires, according to the cache strategy.

If an ETag is provided by the cache strategy, it will be used to generate the fingerprint; otherwise, the last modified date will be used.

If you call req.assetFingerprint() with no arguments, a fingerprint will be registered and generated using the cache strategy on the current URL (i.e. req.url). This is equivalent to req.assetFingerprint(req.url).

Labelled resources

You can call req.assetFingerprint(label, fingerprint, cacheInfo) to manually assign a fingerprint for the specified label. In addition, the HTTP headers returned to the client when this URL fingerprint is requested are specified by the cacheInfo Object.

req.assetFingerprint(label, urlFingerprint, cacheInfo) - Registers a URL fingerprint for a labelled resource.

  • label - a label identifying the resource
  • urlFingerprint - the URL fingerprint for the resource. If a request for this resource is made, static-asset may add caching headers to the response.
  • cacheInfo - an Object containing one or more of these properties:
    • lastModified - the last modified date of the resource
    • etag - the ETag of the resource
    • expires - the expiration date of the resource

Other middleware on the stack can generate their own URL fingerprints for static resources and expose them through req.assetFingerprint. Like this:

//Suppose we are in a middleware function, designed to uglify JS files... 
//stat will refer to the stat Object generated by `fs.stat` 
req.assetFingerprint(javascript_filename, javascript_filename + "?v=" +
    stat.mdate.getTime(), {"lastModified": stat.mdate});

If you call req.assetFingerprint(label) and pass a label, static-asset will return the fingerprint for the resource, as specified by the last corresponding req.assetFingerprint(label, fingerprint, cacheInfo) call. If that file is requested, static-asset will respond by setting the appropriate HTTP headers, according to the cacheInfo Object passed to the last req.assetFingerprint(label, fingerprint, cacheInfo) call.

Default Caching Strategy

static-asset can be fully customized, but it has some basic, reasonably sane default behavior. By default, static-asset does the following:

  • The URL fingerprint of the resource is based on the ETag
  • The ETag is generated based upon the file size and the file's CRC-32 hash.
  • The last modified date is pulled from fs.stat
  • The expires date is set to one year in the future
  • The default strategy relies on [connect.static] ( to load the resource from the filesystem.
  • In development environments (based on process.env.NODE_ENV), the URL fingerprint will be updated whenever the file changes
  • In production environments, the URL fingerprints are cached and cannot change until the server is restarted.

Basic Usage

Usually, this should be good enough to get started.

var express = require('express');
var app = express();
var staticAsset = require('static-asset');
app.use(staticAsset(__dirname + "/public/") );
app.use(express.static(__dirname + "/public/") );
//... application code follows (routes, etc.) 

For example, if you want to include your client-side JavaScript code, simply do this in your Jade or [Blade] ( view:

script(type="text/javascript", src=assetFingerprint("/client.js") )

This will render to something like this:

<script type="text/javascript" src="/client.js?v=1318365481"></script>

Notice that static-asset added a URL fingerprint (the UNIX timestamp 1318365481) to the filename.

More Advanced Usage

You can override the "cache strategy" with your own implementation that might allow you to:

  • Upload the asset to Amazon S3 and generate a URL fingerprint that points to S3
  • Fly in a spaceship to the moon
  • Do something really crazy like generate URL fingerprints that are Base64-encoded MD5-hashes of the names of random lunar craters.