由于链而在同步操作中使用Promise

Question

i have this chain:

phase_one(files).then(phase_two).then(phase_three).then(phase_four);

Each phase will receive this array with object files inside. And inside each phases, i have this default piece of code:

  return Promise.map(files, function(file) {
    // some code here
  }, {
    concurrency: 3000
  });

The problem is.. phase_two is synchronous... but i want still use the chain i shouldn't use the Promise.map.

I would like to know if there is anything to help me with this in bluebird. I search in the docs and i didn't find.

Thanks.

Answer 1

phase_two can just be a function that returns a value. The chain will continue just fine.

phase_one(files).then(phase_two).then(phase_three).then(phase_four);

function phase_two(input) {
    // do something
    return result;
}

A .then() handler can be either synchronous or asynchronous. If it's asynchronous, then it must return a promise. If it's synchronous, it can just return a value which become the value passed to the next part of the chain.

---

The very first link in the chain must return a promise (to start the chain). If phase_one() is synchronous and you want to keep with the structure you had before, then you can just return Promise.resolve(data); from within phase_one() . This will make the return value a promise which will have a .then() handler.