index.js

#!/usr/bin/env node

'use strict';

const f = new Map();
f.set('availpro:1', {id: 1, provider: 'availpro', name: 'Hotel du sentier', rating: 3}); // delete
f.set('synxis:2', {id: 2, provider: 'synxis', name: 'Hotel Opera', rating: 0});        // update
f.set('fastbooking:3', {id: 3, provider: 'fastbooking', name: 'Hotel Garnier', rating: 5}); // skip

const s = new Map();
s.set('synxis:2', {id: 2, provider: 'synxis', name: 'Hotel Opera', rating: 4});        // update
s.set('fastbooking:3', {id: 3, provider: 'fastbooking', name: 'Hotel Garnier', rating: 5}); // skip
s.set('synxis:3', {id: 3, provider: 'synxis', name: 'Hotel Garnier', rating: 5});      // add
s.set('availpro:4', {id: 4, provider: 'availpro', name: 'Hotel Eiffel', rating: 5});     // add

function intersection(f, s) {
   return new Map([...f].filter(([id, data]) => {
    return s.has(id);
  }));  
}

function difference(f, s, opts) {
  let master = s;
  let slave = f;
  
  if (opts.isFetchedMaster) {
    master = f;
    slave = s;
  }
  
  return new Map([...master].filter(([id, data]) => {
    return !slave.has(id);
  }));  
}

function toDelete(f, s) {
  return difference(f, s, { isFetchedMaster: true });
}

function toAdd(f, s) {
  return difference(f, s, { isFetchedMaster: false });
}

function toUpdate(f, s) {
  return intersection(f, s);
}

console.log(toDelete(f, s));
console.log(toAdd(f, s));
console.log(toUpdate(f, s));

package.json

{"name": "unsorted-merge", "version": "0.0.0", "bin": "./index.js"}