How to calculate a hash of a string

Short answer

In Node.js, createHash() from node:crypto calculates a hash. digest('hex') returns it as a hex string:

import { createHash } from 'node:crypto';
 
const hash = createHash('sha256').update('hello').digest('hex');
 
console.log(hash);

Output:

2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824

In the browser

In the browser and in modern Node.js, crypto.subtle.digest() works. It returns bytes that you turn into hex yourself:

const sha256 = async (text) => {
  const bytes = await crypto.subtle.digest('SHA-256', new TextEncoder().encode(text));
  return [...new Uint8Array(bytes)].map((b) => b.toString(16).padStart(2, '0')).join('');
};
 
console.log(await sha256('hello'));

Output:

2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824

A file checksum

A hash of the file content shows whether the file has changed:

import { createHash } from 'node:crypto';
import { readFile, writeFile } from 'node:fs/promises';
 
await writeFile('data.txt', 'version 1');
const checksum = createHash('md5').update(await readFile('data.txt')).digest('hex');
 
console.log(checksum.length);

Output:

Common mistake

Do not store passwords as a plain SHA-256 or MD5 hash: they are fast to brute force. For passwords use special slow functions such as scrypt from node:crypto or bcrypt.

import { randomBytes, scryptSync } from 'node:crypto';
 
const salt = randomBytes(16).toString('hex');
const hash = scryptSync('my password', salt, 64).toString('hex');
 
console.log(hash.length);

Output:

Thanks for reading!

Short answer

In the browser

A file checksum

Common mistake

Functions used in this recipe

Thanks for reading!