Using crypto node.js Library, unable to create SHA-256 Hashes multiple times in rapid succession

Question

I am creating a hash of an auto-incrementing number. I have created two example loops of how I'm trying to achieve this.

When #1 is is run, the first hash is logged to the console and on the second iteration through the loop, the following error is returned. Error: Digest already called

I believe this is due to this reference in the documentation: The Hash object can not be used again after hash.digest() method has been called. Multiple calls will cause an error to be thrown.

How can I create a loop that uses Node's crypto library to create multiple hashes at one time?

 // Reproduce #1
 const crypto = require('crypto');

 const hash = crypto.createHash('sha256');

 for (let i = 0; i < 5; i++) {
   hash.update('secret' + i);

   console.log(hash.digest('hex'));
 }

Answer 1

If the error is "Digest already called", then the idea would be to call the Hash only once. You can do that by creating a fresh Hash instance on each iteration:

const crypto = require('crypto');
for (let i = 0; i < 5; i++) {
    const hash = crypto.createHash('sha256');
    hash.update('secret' + i);
    console.log(hash.digest('hex'));
}

Output:

97699b7cc0a0ed83b78b2002f0e57046ee561be6942bec256fe201abba552a9e
5b11618c2e44027877d0cd0921ed166b9f176f50587fc91e7534dd2946db77d6
35224d0d3465d74e855f8d69a136e79c744ea35a675d3393360a327cbf6359a2
e0d9ac7d3719d04d3d68bc463498b0889723c4e70c3549d43681dd8996b7177f
fe2d033fef7942ed06d418992d35ca98feb53943d452f5994f96934d754e15cb

Answer 2

A clean way to do it without having to repeat const H = crypto.createHash('sha256') on every instance is to use hash.copy() -

 const crypto = require('crypto');
 const hash = crypto.createHash('sha256');

 for (let i = 0; i < 5; i++) {
   hash.update('secret' + i);
   console.log(hash.copy().digest('hex'));
 }

You get the desired output -

e7ebc4daa65343449285b5736ebe98a575c50ce337e86055683452d7d612ac78
3dc562fa371a320efb0cca0ae344c8a5bddfcd3d5191cd124798404b729423c2
7547b5c1992ed566a2125817b2c76ed4a7d3c551232904f886bd954e649e3144
b49247304dc3ef76d9ebfd0482bfc68ab9b7b0fe2007b7c60e03ad6b8123be33
82bc2bcfc528fd55807a981c79e0b6aa430a690b51de79d9d0c5f5627864965b