.spread

.spread(
    [function(any values...) fulfilledHandler]
) -> Promise

Like calling .then, but the fulfillment value must be an array, which is flattened to the formal parameters of the fulfillment handler.

Promise.all([
    fs.readFileAsync("file1.txt"),
    fs.readFileAsync("file2.txt")
]).spread(function(file1text, file2text) {
    if (file1text === file2text) {
        console.log("files are equal");
    }
    else {
        console.log("files are not equal");
    }
});

When chaining .spread, returning an array of promises also works:

Promise.delay(500).then(function() {
   return [fs.readFileAsync("file1.txt"),
           fs.readFileAsync("file2.txt")] ;
}).spread(function(file1text, file2text) {
    if (file1text === file2text) {
        console.log("files are equal");
    }
    else {
        console.log("files are not equal");
    }
});

Note that if using ES6, the above can be replaced with .then() and destructuring:

Promise.delay(500).then(function() {
   return [fs.readFileAsync("file1.txt"),
           fs.readFileAsync("file2.txt")] ;
}).all().then(function([file1text, file2text]) {
    if (file1text === file2text) {
        console.log("files are equal");
    }
    else {
        console.log("files are not equal");
    }
});

Note that .spread() implicitly does .all() but the ES6 destructuring syntax doesn't, hence the manual .all() call in the above code.

If you want to coordinate several discrete concurrent promises, use Promise.join