NodeJS class always return the same value - node.js

Question

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?

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.