[whatwg] Promise.every() arguments

Alec Flett alecflett at chromium.org
Tue Aug 20 13:42:43 PDT 2013

I've been doing a lot of experimentation with Promises using the Blink
implementation. I've frequently hit an issue with the .every() / .any() /

the problem is that they support a variable number of arguments. This seems
very developer friendly in theory, as per the docs:

Promise.every(fetchJSON(foo), fetchJSON(bar), fetchJSON(baz));

This is great the first time you play with it on your local developer

The problem arises in practice: it's very common to build up arrays of N
promises, and then tie them all together. Even if your own API uses
varargs, using Promise.every breaks down.

function getDocuments(requests) {
    var pending = [];
    for (var i = 0; i < requests.length; ++i) {
        var url = extractUrl(requests[i]);

    // nope, this won't work!
    // return Promise.every(pending);

    // only this works
    Promise.every.apply(Promise, pending);

this is how (and why) kiskowal's Q works with an array as the single



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