promise.all inside a forEach loop — everything firing at once

Question

In a Node app, I need to iterate through some items in a synchronous fashion, but some of the operations inside the loop are asynchronous. My code right now looks like so:

Answer 1

How about keeping the forEach...

var stopAllProcessingOnServerLowValue= false;

function someAPIpromise(){
    var arr = [
        {id:123, urlVal:null},
        {id:456, urlVal:null},
        {id:789, urlVal:null},
        {id:101112, urlVal:null}
    ];

    return new Promise(function(resolve){
        setTimeout(function(){
            resolve(arr)
        }, 3000);
    })
}

function extractSomeValueRemotely(url){
    return new Promise(function(resolve, reject){
        console.log("simulate an async connection @ %s to request a value", url);
        setTimeout(function(){
            var someRandom = Math.round(Math.random()*7) + 1;
            console.log("%s responded with %s", url, someRandom);
            if(someRandom > 4){
                resolve(someRandom);
            }
            else{
                var issue = "Urls result is too low ("+someRandom+" <= 4).";
                console.warn(issue+".It will be set to -1");
                if(stopAllProcessingOnServerLowValue){
                    reject(issue+".Operation rejected because one or mole server results are too low ["+someRandom+"].");
                }
                else{
                    resolve(-1);
                }
            }
        }, 1500*Math.round(Math.random()*7) + 1);
    });
}

function addAnotherExtraParamToItem(_item){
    return new Promise(function(resolve, reject){
        setTimeout(function(){
            console.log("setting extra2 on %s", _item.id);
            _item['extra'] = "additional_processing_"+_item.id;
            resolve(_item);
        }, 1500*Math.round(Math.random()*5) + 1);
    });
}

function addOrderIndexToItem(_item, _order){
    return new Promise(function(resolve, reject){
        setTimeout(function(){
            console.log(">> setting order %s on %s",_order,  _item.id);
            _item['order'] = _order;
            resolve(_item);
        }, 1500*Math.round(Math.random()*3) + 1);
    });
}

someAPIpromise().then(function(items){

    var perItemPromises = [];
    items.forEach(function(item, idx){

        perItemPromises.push(

            new Promise(function(pulseItemResolve, pulseItemReject){
                var itemStepsPromises =  [];
                itemStepsPromises.push(addAnotherExtraParamToItem(item));

                itemStepsPromises.push(extractSomeValueRemotely("http://someservice:777/serve-me")
                    .catch(
                        function(reason){
                            //the entire item will be rejected id
                            pulseItemReject(reason);
                        })
                );

                itemStepsPromises.push(addOrderIndexToItem(item, idx));

                //promise that ensure order of execution on all previous async methods
                Promise.all(itemStepsPromises).then(function(values){
                    //0 - first is result from addAnotherExtraParamToItem
                    var theItem = values[0]; //it returns the item itself
                    //urlVal has not been set yet

                    // 1 - second promise return the url result
                    var serverResult = values[1];

                    //2 - third promise add the order index but we do not care to inspect it because theItem reference in value[0] has been already updated.
                    // console.info(values[2]);

                    //sets the url result in the item
                    theItem.urlVal = serverResult;
                    console.log("urlVal set to:", theItem.urlVal);

                    //resolve the prepared item
                    pulseItemResolve(theItem);

                });
            })
                .catch(function(reason){
                    //escalate error
                    throw new Error(reason);
                })
        )

    });

    Promise.all(perItemPromises).then(function(resultsInAllItems){
        console.info("Final results:");
        console.info(resultsInAllItems);
    }).catch(function(finalReject){
        console.error("Critical error:",finalReject);
    })


});