Steps for ensuring a promise is fulfilled in Node.js and Firebase

Question

Steps for ensuring a promise is fulfilled in Node.js and Firebase

I've been struggling with this issue for quite some time now and can't seem to figure it out.

g_globalList.once("value").then(function(tickList){
    var multiPaths = [];    
    tickList.forEach(function(ticker){
        ticker.val().forEach(function(path){
            multiPaths.push(path);
        });
    });
    return multiPaths;        
}).then(function(multiPaths){
    var myObj = {};
    multiPaths.forEach(function(path){
        var ticker = path.substr(path.lastIndexOf("/")+1, 40);
        console.log("adding " + ticker);

        ****this is another promise and make my "myObj" to print blank****

        db.child("symbols/NSE/" +ticker).once('value').then(function(data){
            if(data.exists()){
                myObj[path] = data.val();
            }       
        });
    });
    return myObj;
}).then(function(myObj){
    console.log(myObj);
});

Is there any way that I can delay the final "console.log(myObj)" until after all promises have been completed?

javascript node.js firebase firebase-realtime-database

Answer 1

Answer №1

Utilizing Promise#all allows you to wait for all Promises to resolve. Take a look at the code snippet below for an example (not tested, but it might give you some insight on how to tackle your issue):

var allPaths = [];

g_globalList.once("value").then(function(tickList){  
    return Promise.all(
   //map will create a array of the returned values (Promises in this case)
        tickList.map(function(ticker){
            return ticker.val();
        })
    );
}).then(function(values){//values represents all then results
    allPaths = values; //store all paths for later use
    return Promise.all(
        //map will create a array of returned values (Promises in this case)
        values.map(function(path){

            var ticker = path.substr(path.lastIndexOf("/")+1, 40);
            return db.child("symbols/NSE/" +ticker).once('value');
        })
    );
}).then(function(values){//values represents all then results
    var myObj = {}; //let's create an object

    for(var i = 0; i < allPaths.length; i++){ //for each path
        var path = allPaths[i];
        //extract the ticker name again
        var ticker = path.substr(path.lastIndexOf("/")+1, 40);

        //check your data
        var data = values[i];
        if(data.exists()){
            //add to the object
            myObj[path] = data.val();
        }      
    }
    //return the object
    return myObj;
})
.then(function(myObj){
    //hopefully, the object is ready here
    console.log(myObj);
});

Answer 2

Utilizing Promise#all allows you to wait for all Promises to resolve. Take a look at the code snippet below for an example (not tested, but it might give you some insight on how to tackle your issue):

var allPaths = [];

g_globalList.once("value").then(function(tickList){  
    return Promise.all(
   //map will create a array of the returned values (Promises in this case)
        tickList.map(function(ticker){
            return ticker.val();
        })
    );
}).then(function(values){//values represents all then results
    allPaths = values; //store all paths for later use
    return Promise.all(
        //map will create a array of returned values (Promises in this case)
        values.map(function(path){

            var ticker = path.substr(path.lastIndexOf("/")+1, 40);
            return db.child("symbols/NSE/" +ticker).once('value');
        })
    );
}).then(function(values){//values represents all then results
    var myObj = {}; //let's create an object

    for(var i = 0; i < allPaths.length; i++){ //for each path
        var path = allPaths[i];
        //extract the ticker name again
        var ticker = path.substr(path.lastIndexOf("/")+1, 40);

        //check your data
        var data = values[i];
        if(data.exists()){
            //add to the object
            myObj[path] = data.val();
        }      
    }
    //return the object
    return myObj;
})
.then(function(myObj){
    //hopefully, the object is ready here
    console.log(myObj);
});

Answer 3

Answer №2

Optimize your code by substituting forEach with map on multiPaths. Make sure to capture each db.child call's return value and nest the map function within a Promise.all() for better efficiency.

Answer 4

Optimize your code by substituting forEach with map on multiPaths. Make sure to capture each db.child call's return value and nest the map function within a Promise.all() for better efficiency.

Steps for ensuring a promise is fulfilled in Node.js and Firebase

Answer №1

Answer №2

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