Serialize a list of js promises call

Question

what's the most convenient way to serialize a bunch of promised function call?

var promised_functions = [
 fn1,  // call this 
 fn2,  // if previous resolved call this
 fn3   // if previous resolved call this
];
q.serialize_functions(promised_functions)
.then(function(){
 // if all promises resolved do some
})

Answer 1

You can find the solution in the documentation:

promised_functions.reduce(Q.when, Q()).then(function () {
    // if all promises resolved do some
});

Skip down to the "Sequences" section of the documentation. To copy it verbatim:

---

If you have a number of promise-producing functions that need to be run sequentially, you can of course do so manually:

return foo(initialVal).then(bar).then(baz).then(qux);

However, if you want to run a dynamically constructed sequence of functions, you'll want something like this:

var funcs = [foo, bar, baz, qux];

var result = Q(initialVal);
funcs.forEach(function (f) {
    result = result.then(f);
});
return result;

You can make this slightly more compact using reduce:

return funcs.reduce(function (soFar, f) {
    return soFar.then(f);
}, Q(initialVal));

Or, you could use th ultra-compact version:

return funcs.reduce(Q.when, Q());

---

There you have it. Straight from the horse's mouth.