Promise chain graph

gistfile1.js

(({timeout1, timeout2}) => {
const startOp = (name, timeout) => () => {
  console.log(name + ' started at ' + Date.now())
  return new Promise(function(resolve) {
    setTimeout(function() {
      resolve();
    }, timeout);
  });
}

const start = Date.now();
const op1 = startOp('StartOp1', timeout1)();
const op2 = startOp('StartOp2', timeout2)();
op1.then(function() {
  // Fires when op1 is successful; doesn't care about op2
  console.log("op1 done after " + (Date.now() - start) + "ms");
});
op2.then(function() {
  // Fires when op2 is successful; doesn't care about op1
  console.log("op2 done after " + (Date.now() - start) + "ms");
});
Promise.all([op1, op2]).then(function() {
  // Fires when BOTH ops are successful
  console.log("both done after " + (Date.now() - start) + "ms");
});
})({
  timeout1: 1000,
  timeout2: 2000
})

// We can has as many points to branch as want. Thus we can make a graph of executions
(({timeout1, timeout2}) => {
const startOp = (name, timeout) => async () => {
  console.log(name + ' started at ' + Date.now())
  return new Promise(function(resolve) {
    setTimeout(function() {
      resolve();
    }, timeout);
  });
}

const start = Date.now();
const op1 = startOp('StartOp1', timeout1)();
const op2 = op1.then(() => startOp('StartOp2', timeout2)());
Promise.all([op1, op2]).then(function() {
  // Fires when BOTH ops are successful
  console.log(Date.now() + " both done after " + (Date.now() - start) + "ms");
});
op1.then(function() {
  // Fires when op1 is successful; doesn't care about op2
  console.log(Date.now() + " op1 done after " + (Date.now() - start) + "ms");
});
op2.then(function() {
  // Fires when op2 is successful; doesn't care about op1
  console.log(Date.now() + " op2 done after " + (Date.now() - start) + "ms");
});
})({
  timeout1: 1000,
  timeout2: 2000
})

Если у тебя есть цепочка асинхронных операций - намного удобнее использовать async/await:

var res1 = await operation1(input);
if (res1 == "good")
{
    var res2 = await operation2(res1);
    await Task.WhenAll(operation3_1(res2), operation3_2 (res2));
}
await operation4(res1);

С continuation-цепочками это выглядело бы так:

operation1(input)
    .ContinueWith(
        task =>
        {
            if (task.Result == "good")
            {
                return operation2(task.Result)
                    .ContinueWith(task2 => Task.WhenAll(operation3_1(task2.Result), operation3_2(task2.Result)))
                    .ContinueWith(_ => task);
            }
            return task
        })
    .ContinueWith(task => operation4(task.Result));