map-semigroupoid.ts

function mapCompose<A, B, C>(mab: Map<A, B>, mbc: Map<B, C>): Map<A, C> { 
  const mac: Map<A, C> = new Map();

  mab.forEach((value, key) => { 
    const finalValue = mbc.get(value);

    if (finalValue !== undefined) {
      mac.set(key, finalValue);
    }
  });

  return mac;
}

const mab: Map<number, string> = new Map();
const mbc: Map<string, boolean> = new Map();

mab.set(0, 'zero');
mab.set(1, 'one');
mab.set(3, 'three');

mbc.set('zero', true);
mbc.set('two', false);
mbc.set('three', false);

const mac = mapCompose(mab, mbc);

console.log(mac.get(0))
console.log(mac.get(1))
console.log(mac.get(2))
console.log(mac.get(3))