node-hash-and-partition.js

// See: https://medium.com/@promentol/cryptography-for-javascript-node-js-developers-part-1-hash-function-86d119c7304

function hash(data, digest = 'hex') {
  return require('crypto').createHash('sha256').update(data).digest(digest)
}

// ('foo', 10) => 6
// ('bar', 10) => 6
// ('zz', 10) => 2
// ('foo', 6) => 2
// ('bar', 6) => 4
// ('foo', 20) => 16
// NOTE: probably better to use https://en.wikipedia.org/wiki/Consistent_hashing
function selectPartition(data, nPartitions) {
  return parseInt(hash(data), 16) % nPartitions
}