Calculate SHA-256 hash in JavaScript

The SHA-256 algorithm is a widely used hash function producing a 256-bit hash value. It is used in many security applications and protocols, including TLS and SSL, SSH, PGP, and Bitcoin.

Calculating a SHA-256 hash in JavaScript is easy using native APIs, but there are some differences between the browser and Node.js. As the browser implementation is asynchronous, both of the examples provided will return a Promise for consistency.

Browser

In the browser, you can use the SubtleCrypto API to create a hash for the given value. You first need to create a new TextEncoder and use it to encode the given value. Then, pass its value to SubtleCrypto.digest() to generate a digest of the given data, resulting in a Promise.

As the promise resolves to an ArrayBuffer, you will need to read the data using DataView.prototype.getUint32(). Then, you need to convert the data to its hexadecimal representation using Number.prototype.toString(). Add the data to an array using Array.prototype.push(). Finally, use Array.prototype.join() to combine values in the array of hexes into a string.

const hashValue = val =>
  crypto.subtle
    .digest('SHA-256', new TextEncoder('utf-8').encode(val))
    .then(h => {
      let hexes = [],
        view = new DataView(h);
      for (let i = 0; i < view.byteLength; i += 4)
        hexes.push(('00000000' + view.getUint32(i).toString(16)).slice(-8));
      return hexes.join('');
    });

hashValue(
  JSON.stringify({ a: 'a', b: [1, 2, 3, 4], foo: { c: 'bar' } })
).then(console.log);
// '04aa106279f5977f59f9067fa9712afc4aedc6f5862a8defc34552d8c7206393'

Node.js

In Node.js, you can use the crypto module to create a hash for the given value. You first need to create a Hash object with the appropriate algorithm using crypto.createHash(). Then, use hash.update() to add the data from val to the Hash and hash.digest() to calculate the digest of the data.

For consistency with the browser implementation and to prevent blocking on a long operation, we'll return a Promise by wrapping it in setTimeout().

import { createHash } from 'crypto';

const hashValue = val =>
  new Promise(resolve =>
    setTimeout(
      () => resolve(createHash('sha256').update(val).digest('hex')),
      0
    )
  );

hashValue(JSON.stringify({ a: 'a', b: [1, 2, 3, 4], foo: { c: 'bar' } })).then(
  console.log
);
// '04aa106279f5977f59f9067fa9712afc4aedc6f5862a8defc34552d8c7206393'

Notes

• The two implementations are not compatible with each other. You cannot use the browser implementation in Node.js and vice versa.
• Both implementations should produce the same result for the same input.