Promise.all in Node is undefined

Question

I'm playing around with promises in Node.js and am trying to use Promise.all. I'm pushing three functions that return a promise into an array and then calling Promise.all but the all's resolve is never hit. On the debugger, it also says that Promise.all is "undefined".

Why is Promise.all never returning and why does it show up as "undefined"?

Relevant part of the code:

var updates = [];
updates.push(data.updateItemCondition(characterID, specificItemID_toUse, newCondition));
updates.push(data.updateCharacterLoot(characterID, newValue));
updates.push(data.updateSharedLoot(lootUpdateChange));


Promise.all(updates).then(function (success) {
    resolve("Item successfully used");
}, function (error) {
    resolve("Failed to use item " + error.toString());
});

All three functions look something like the below and using the debugger I can see that all three resolves are hit (and all three corresponding files on io.writeFile are updated on disk)

data.updateSharedLoot= function (lootUpdateChange) {
    return new Promise(function (resolve, reject) {
        //some logic
        io.writeFile(...,function(callbackSuccess){
            resolve(callbackSuccess);
        });
    });
}

`Why is Promise.all never returning` because `Promise.all is "undefined"` - you can't "return" from a function that doesn't exist - are you sure you haven't "overloaded" Promise with some broken Promise implementation — Jaromanda X, Dec 23 '16 at 23:32
All I have is require('promise'). I put a breakpoint at the very beginning of my application entry point and can see that Promise.all is already undefined, so it does not look like it was "overloaded" later. The code completion also does not autocomplete Promise.all. For the record.. node -v is v4.4.7 — YuriW, Dec 23 '16 at 23:47

score 1 · Answer 1 · edited May 23 '17 at 11:59

That's strange because I have Promise.all defined even on old Node 0.12. On Node 0.10 I have Promise not defined. I don't think there's a version with Promise but without Promise.all. Maybe you're doing:

Promise.all = undefined;

What you should have undefined is the resolve function. Here:

Promise.all(updates).then(function (success) {
    resolve("Item successfully used");
}, function (error) {
    resolve("Failed to use item " + error.toString());
});

you don't have any resolve to call. Don't you mean console.log?

Promise.all(updates).then(function (success) {
    console.log("Item successfully used");
}, function (error) {
    console.log("Failed to use item " + error.toString());
});

Also here:

data.updateSharedLoot= function (lootUpdateChange) {
    return new Promise(function (resolve, reject) {
        //some logic
        io.writeFile(...,function(callbackSuccess){
            resolve(callbackSuccess);
        });
    });
}

the first parameter to your callback is probably an error, so you should:

data.updateSharedLoot= function (lootUpdateChange) {
    return new Promise(function (resolve, reject) {
        //some logic
        io.writeFile(...,function(error, callbackSuccess) {
            if (error) {
                reject(error);
            } else {
                resolve(callbackSuccess);
            }
        });
    });
}

But still I would suggest using a promised version of I/O like fs-promise if you're doing promises anyway. Your function that returns a promise could be as simple as:

var fsp = require('fs-promise');

data.updateSharedLoot = function (lootUpdateChange) {
    return fsp.writeFile(...);
};

See this answer for more details.

I'm sorry, I forgot to mention that this is all within another promise. In either case, I did put breakpoints within both the functions in the Promise.all(...).then and they are never hit. Thanks for the suggestions, learning from mistakes already :) — YuriW, Dec 23 '16 at 23:02

Promise.all in Node is undefined

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