Node.js: function to create an hash from a file (path or Buffer)

getFileHash.js

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

/**
 * It calculates the hash of a file
 * @param {string} hashName type of hash (md5, sha1, etc)
 * @param {string|Stream} file a file's path or a readable stream
 * if it's been already opened somewhere else
 */
function getFileHash(hashName, file) {
    return new Promise((resolve, reject) => {
        const hash = crypto.createHash(hashName);
        let stream;

        if (typeof file === 'string') {
            stream = fs.createReadStream(file);
        } else if (file instanceof Readable) {
            stream = file;
        } else {
            throw new Error('Second argument must be a string or a readable stream');
        }

        stream.on('error', (err) => reject(err));
        stream.on('data', (chunk) => hash.update(chunk));
        stream.on('end', () => resolve(hash.digest('hex')));
    });
}