Basic node.js - variable and Mongoose scope

Question

the console.log(workingWeekdaysVar) line; is outside the findOne's scope, and the variable was declared outside it too, yet it's giving me null ...

when i put console.log(workingWeekdaysVar); inside the findOne's scope, it does give the right output, but this is useless for me because I wanna use workingWeekdaysVar elsewhere below.

The two commented out lines are the 2nd approach i attempted to do, but it gave me an undesirable output because this whole code is inside a complicated for loop.

How can I simply pass the fetched value of workingWeekdaysVar out of the scope?

    var workingWeekdaysVar = [];

                    buyerSupplierFisModel.findOne(filter).then(function (combo) {

                        workingWeekdaysVar = combo.workingWeekdays;

                         //server.getWorkingWeekdays = function () { return combo.workingWeekdays };

                    });

   console.log(workingWeekdaysVar);

//console.log(server.getWorkingWeekdays());

Miguel Calderón · Accepted Answer · 2018-03-16 12:12:37Z

1

findOne() is an asynchronous function (it returns a promise object). This means that it returns inmediately and your next code line is run (in this case, console.log(workingWeekdaysVar);. But, since the function isn't done yet, workingWeekdaysVar is empty, and it will be empty until findOne() has done its job and returned the results in the provided chained callback .then(function (combo) {....

So if you want to do anything with the results, you'll have to do it in the callback. One option to this would be to use async / await:

(async () => {
    try {
        const { workingWeekdaysVar } = await buyerSupplierFisModel.findOne(filter)
        console.log(workingWeekdaysVar)
    } catch (e) {
        console.log(`Error: ${e}`);
    }
})()

answered Mar 16, 2018 at 12:12

Miguel Calderón

3,1011 gold badge20 silver badges19 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

terary · Accepted Answer · 2018-09-28 02:32:42Z

0

Re-arranging your code a bit:

let doToResponse = (combo)=>{
 workingWeekdaysVar = combo.workingWeekdays; 
 console.log(workingWeekdaysVar);
}
 buyerSupplierFisModel.findOne(filter).then(function (combo) {
                        doToResponse(combo)
                    });

good for re-usability

My personal favorite:

buyerSupplierFisModel.findOne(filter).then(combo=> {
    workingWeekdaysVar = combo.workingWeekdays; 
    console.log(workingWeekdaysVar);
});

The important thing is keep in mind, as Miguel Calderón says.. findOne - returns a promise. At that point you have another thread with different local (Lexical?) scope

answered Sep 28, 2018 at 2:32

terary

1,13815 silver badges31 bronze badges

Collectives™ on Stack Overflow

Basic node.js - variable and Mongoose scope

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related