JS concurrency _stuff_

concurrency.ts

interface Person {
  name: string;
  age: number;
}

const people: Person[] = [{ name: "Bob", age: 100 }, { name: "Jane", age: 50 }];

const findPeople = (candidate: string): Promise<Person[]> => {
  return new Promise(resolve => {
    const timeout = Math.floor(Math.random() * 100);

    setTimeout(() => {
      console.log("Finding: ", candidate);
      console.log("After: ", timeout);

      resolve(people.filter(({ name }) => candidate === name));
    }, timeout);
  });
};

const fetchPeople = async (
  candidates: string[]
): Promise<{ [key: string]: Person[] }> => {
  const results: [string, Person[]][] = await Promise.all(
    candidates.map(async candidate => {
      const found = await findPeople(candidate);
      const result: [string, Person[]] = [candidate, found];
      return result;
    })
  );
  return results.reduce(
    (acc, [name, peeps]) => ({
      ...acc,
      [name]: peeps
    }),
    {}
  );
};

const fetchPeopleTwo = async (
  candidates: string[]
): Promise<{ [key: string]: Person[] }> => {
  return candidates.reduce(async (acc, candidate) => {
    const results = await acc;
    const peeps = await findPeople(candidate);
    return {
      ...results,
      [candidate]: peeps
    };
  }, Promise.resolve({}));
};

const time = async (action: () => Promise<void>): Promise<number> => {
  const start = Date.now();
  await action();
  const end = Date.now();
  return end - start;
};

const main = async () => {
  console.log("Map reduce");
  const mapReduceDuration = await time(async () => {
    const result = await fetchPeople(["Bob", "Jane"]);
    console.log(result);
  });
  console.log("Took", mapReduceDuration);

  console.log("\nReduce");
  const reduceDuration = await time(async () => {
    const result = await fetchPeopleTwo(["Bob", "Jane"]);
    console.log(result);
  });
  console.log("Took", reduceDuration);
};

// EXAMPLE OUTPUT:
//
// Map reduce
// Finding:  Jane
// After:  26
// Finding:  Bob
// After:  42
// { Bob: [ { name: 'Bob', age: 100 } ],
//       Jane: [ { name: 'Jane', age: 50 } ] }
// Took 49

// Reduce
// Finding:  Bob
// After:  39
// Finding:  Jane
// After:  2
// { Bob: [ { name: 'Bob', age: 100 } ],
//       Jane: [ { name: 'Jane', age: 50 } ] }
// Took 46

main();