Serpa (series & parallel)

Serpa is a small utility library for promise chaining.

Promises may be chained in series or parallel:

var serpa = require(serpa),
    series = serpa.series,
    parallel = serpa.parallel,
    split = serpa.split;

//Being task1, task2a, task2b and task3 functions
//that either return promises for async taks
//or a value, then:
var work = series( //configure the work to be done
    task1,
    parallel(task2a, task2b),
    split(task3)
  );

work() //do the work
  .then(
    function (result) {
      console.log("Work finished with result" + result);
    },
    function (err){
      console.log("Some task failed with err: " + err);
    });

Series

Series execution of the tasks. The result of each task is passed to the next task.

function addTwo(x) {
  return x  + 2;
}
function addThree(x) {
  var defer = q.defer();
  setTimeout(function () {
      defer.resolve(x + 3);
    },1000);
  return defer.promise();
}

var work = series(
    addTwo,
    addThree
  );

work(1).then(function (result) {
  console.log(result); //eventually logs 6
});

Parallel

All the tasks are executed in parallel. The entry value is passed to each task.

function addTwo(x) {
  return x  + 2;
}
function addThree(x) {
  var defer = q.defer();
  setTimeout(function () {
      defer.resolve(x + 3);
    },1000);
  return defer.promise();
}

var work = parallel(
    addTwo,
    addThree
);

work(1).then(function (result) {
  console.log(result); //eventually logs [3, 4];
});

Split

The tasks are executed for each element of the array that should be the input to the chain.

function addTwo(x) {
  return x  + 2;
}
function addThree(x) {
  var defer = q.defer();
  setTimeout(function () {
      defer.resolve(x + 3);
    },1000);
  return defer.promise();
}

var work = split(
    addTwo,
    addThree
);

work([1,2,3]).then(function (result) {
  console.log(result); //eventually logs [6, 7, 8];
});

Preserve

The tasks are executed and then the original value is returned

var work = preserve(
  series(
    split(
      addTwo, addThree
    )
  )
);

work([1,2]).then(function (result){
  console.log(result); //eventually logs [1,2];
});