Promise.all在同一阵列上

Question

I'm looking at promises-based code that does something like this:

var promises = [];
function eventHandler(e)
{
    promises.push(getSomeData(e.opts));

    Promise.all(promises)
        .then(...)
        .then(function()
        {
            promises = [];
        });
}

Shouldn't the Promise.all based promise execute as many times as the eventHandler is called?

EDIT: what's happening here is the event handler gets called a few times and the previous promises are not finished yet. I need a way to be able to extend the list of promises and have only one final then run.

Answer 1

Update, OP has clarified they'd like to wait for all promises added before the original ones resolved as well - .all does not do this. Instead you can use thenable chaining.

var p = Promise.resolve([]); // create empty array promise, `when` in dojo
function eventHandler(e){
    p = p.then(function(value){ // chain off the last value
        return getSomeData(e.opts).then(function(single){
            return value.push(single); // add to the array
        });
    });
}

This will add an item to the array each time the eventHandler is called - every time you .then it you will get the current values and not the last ones - but you can .then it as many times as you'd like. You can for example chain on when no events happened since the chaining time by:

var p2 == p;
p.then(function(results){
    if(p !== p2) return p; // wait in case more events happened, but no more
    return results;
});

Or wait for as long as you'd like:

function noMoreAddedInterim(){
   var p2 = p;
   return p.then(function(results){
       if(p2 !== p) return noMoreAddedInterim(); // changed
       else return results; // no more added
   });
 }

---

You have a race condition, you're calling Promise.all and only cleaning the array later so many promises are in the results twice or more.

Instead - put promises in a temporary variable, .all that and clear promises before the .then . Since you're adding promises one at a time you probably don't even need the .all here.

Also, you should attach a .catch handler to not miss any errors.