Concurrent, Parallel and Sequential operations using Javascript Promise.

concurrent.js

async function concurrent() {
  const fetchA = A.fetch();
  const fetchB = B.fetch();
  
  const responseA = await fetchA;
  const responseB = await fetchB;
  
  return {a: responseA, b: responseB};
}

parallel.js

async function parallel() {
  const fetchA = A.fetch;
  const fetchB = B.fetch;
  
  const [responseA, responseB] = await Promise.all([fetchA(), fetchB()]);
  
  return {a: responseA, b: responseB};
}

sequential.js

async function sequential() {
  const responseA = await A.fetch();
  const responseB = await B.fetch();
  
  return {a: responseA, b: responseB};
}