1.1.0 • Public • Published


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Module for digesting hashes of local and remote resources in order to provide element integrity.

$ npm install -g virtue

Originally conceptualized to generate hashes for the HTML integrity attribute (following the W3C Candidate Recommendation 12 November 2015) virtue remains available to generate the hashes of both local and remote resources, in-batch, with the command line or within your Node.js applications.


Node.js >=4.0.0 is required as Promises, lets, and consts are incorporated, legacy support for Node <4.0.0 is in the works. The default hash used in digestion is sha256, but can include any other hash available to Node.js' Crypto library. Current remote protocols include HTTP and HTTPS and remote resources must specify their protocol (http:// or https://.)

Command Line Interface

Installing virtue globally will allow you to digest resources on the command line (the order of arguments does matter.)

$ virtue [--json] [--help] [--hashes] [[--hash] ..] <resource [[--hash] ..]>
  • --json will force all output (help, errors, results, etc.) to be formatted in JSON. Not for human-readability, but could be useful to your other non-Node.js applications.
  • --help will generate some general system information to diagnose any possible conflicts while also providing some directions, similar to what you're reading now.
  • --hashes will return the same list of available hashes as require('crypto').getHashes(), possibly useful again to your other non-Node.js applications.
  • [[--hash] ..] can be one or multiple hashes from --hashes. These together will be the default set of hashes virtue will use. If a --hash is invalid or not available, then an error will be returned before any digesting is done. These specifications are not required but can be useful to you when you have multiple resources and a specified list of --hash(s).
  • resource [[--hash] ..] represents a file resource either locally or remotely. Any --hash(s) after the resource will tell virtue to apply those to that resource instead of the defaults. At least one resource is required, trailing hashes are not. If any specified hash is invalid or unavailable, then virtue returns an error specifying so.

Below is a command line example of:

  • Setting a default hash of sha512.
  • Including a remote file with a specific hash of sha256
  • Including a local file that will default to sha512.
$ virtue --sha512 --sha256 jquery.min.js
Printing digests...
    sha256 === GeBl6q3yb1jA4QgaLg5kRQ7sKYPuuwj5mOyqyshkKkc=

    sha512 === MkM2us1noHhdh0LTfWnwckBSRMLMVY0+KxF76Zq3EbIvreEAgYFH8q3G73YJwKYwfSBuoIbEUmFm/4Omv8iP3w==


Here is something similar to the above, but with the --json flag prepended.

$ virtue --json --sha512 jquery.min.js


When using virtue programmatically, your application will receive a new Promise to work with.

  (results) => console.log(JSON.stringify(results,null,"  ")),
  (error) => console.log("Uh-oh!",error)

The above results will contain an object structured like below, ordered according to the arguments originally provided.

    "src": "/downloaded/locally/jquery/3.0.0-alpha1/jquery.min.js",
    "digests": {
      "sha256": "GeBl6q3yb1jA4QgaLg5kRQ7sKYPuuwj5mOyqyshkKkc="
    "src": "",
    "digests": {
      "sha256": "GeBl6q3yb1jA4QgaLg5kRQ7sKYPuuwj5mOyqyshkKkc="

Programmatic API

virtue(resource[, ...])

Every resource argument provided, as either a string or an array, will be used in digestion.

Default Hash Digestion

The below will result with sha256 digests of both resources. Because no hashes are specified, the default hash is assumed.


Specified Hash Digestion

The below, because a hash is specified, will override the default hash with the specified and will, in this case, result with sha512 digests.


Specified Multiple Hashes Digestion

Finally, should your application want to include multiple digests, specify what you would want digested and returned, using an array of hashes (an array of one hash is the same as just a hash string, like in the example before.)



The hashes provided, as either a string or an array, will be set as the default to be used in digestion and will return true. If a hash provided in hashes is not valid, then this will return false and will not change the default.

  // these will return true
  // these will return false
  virtue.defaultHashes()),                    // empty
  virtue.defaultHashes([])),                  // empty
  virtue.defaultHashes(true)),                // invalid hash
  virtue.defaultHashes("invalid")),           // invalid hash
  virtue.defaultHashes(["sha256",true])),     // array w/invalid hash
  virtue.defaultHashes(["sha256","invalid"])// array w/invalid hash


npm i virtue

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