NodeJS class always return the same value

Question

NodeJS class always return the same value

In NodeJS, I tried to create 2 object of a same class. However, these 2 object are always the same despite having different values. Here is the class.

function reading(){
    var readingArr = [];
};

reading.prototype.dbValue = function(counter, limit, type, mIndex) { 
    db.data.find({ 'type': type }).limit(limit).sort({timestamp:-1}).skip(counter, function(err, docs){
        readingArr = [];

        if( docs != 'undefined'  ){
            for(var i=0; i<limit; i++){
                readingArr.push(docs[i].measurement[mIndex].value.toFixed(2)); //2 Decimal Placet;
            }
        }
    });

    if(typeof readingArr == 'undefined'){
        readingArr = [];
    }
    return readingArr;
 };

Here is the object creation.

var spo2 = new reading(); 
var spo2Arr = spo2.dbValue(0, 5, 'Oximeter', 1);

var temp1 = new reading(); 
var temp1Arr = temp1.dbValue(0, 5, 'Temperature', 0);

Both spo2Arr and temp1Arr return the same value despite having different value in the database. Example

spo2Arr: 98.00
temp1Arr: 98.00

spo2Arr: 37.91
temp1Arr 37.91

May I know how to create two unique object in NodeJS?

node.js

Answer 1

You're performing an asynchronous function call which is not going to complete until some time after dbValue() has finished executing.

Try this:

reading.prototype.dbValue = function(counter, limit, type, mIndex, cb) { 
  db.data.find({ 'type': type }).limit(limit).sort({timestamp:-1}).skip(counter, function(err, docs){
    if (err)
      return cb(err);

    var readingArr = [];

    if (docs !== undefined) {
      for (var i = 0; i < limit; i++)
        readingArr.push(docs[i].measurement[mIndex].value.toFixed(2));
    }

    cb(null, readingArr);
  });
};

Then you might use it like:

var spo2 = new reading();
spo2.dbValue(0, 5, 'Oximeter', 1, function(err, spo2Arr) {
  // check for `err`, if it's falsey, use `spo2Arr`
});

var temp1 = new reading();
temp1.dbValue(0, 5, 'Temperature', 0, function(err, temp1Arr) {
  // check for `err`, if it's falsey, use `temp1Arr`
});

If the temperature readings depend on the oximeter readings, you'll have to mode the temperature reading code inside the oximeter reading callback or you can use a module like async to help structure your control flow.