While working on a project, I wanted to do an integrity check of a file that I was referencing. So, I needed to know how to get the hash of a file in Node.js. And this post is about that.

We will use the fs and crypto modules that are available in Node.js to get the hash of a file. We will be using the createReadStream method of the fs module to read the file and get its contents. After we are done reading it, we will call the the getHash() method of the crypto module to calculate the hash of the file.

const fs = require('fs');
const crypto = require('crypto');

const getHash = path => new Promise((resolve, reject) => {
 const hash = crypto.createHash('sha256');
 const rs = fs.createReadStream(path);
 rs.on('error', reject);
 rs.on('data', chunk => hash.update(chunk));
 rs.on('end', () => resolve(hash.digest('hex')));
})

Then, we can use the getHash method to get the hash of a file. It is worth mentioning that we could have used various algorithms for hashing our file, like md5, sha1 and sha256. sha256 would be the more robust algorithm but a bit slower than the other less secure ones. For the digest method, we could have used hex or base64 depending on how we want to output the hash. We can use the above method like so:

(async () => {
  try {
    const hashValue = await getHash('path/to/file');
    console.log(hashValue);
  } catch (error) {
    console.error('Error:', error);
  }
})();

And that is all to the code and its explanation. If you have any questions, feel free to drop a comment below.