Filter keys in Object - node.js

Question

I am trying to implement a simple extraction function that connects to the Poloniex.returnTicker endpoint and, extract the 'last' key for any currency pairs starting with 'BTC'. There are a number of keys starting with 'BTC' but, my extraction function is stopping after returning exactly one key. I am mapping the extracted data in an object in the following manner:
extracted = {
BTC: {
STR: {
lastPrice: price
},
ETH: {
lastPrice: price
}, //...
}, //...
}
I wrote the following function for extraction:
module.exports = {
extractData: (tickerdata, marker) => {
if(!!!marker){
marker = 'BTC';
}
return new Promise((res, rej) => {
let currentBuffer = {};
Object.keys(tickerdata)
.filter((key) => {
return key.startsWith(marker);
})
.forEach((filtKey) => {
let c = filtKey.split('_'),
src = c[0],
dst = c[1];
currentBuffer[src] = {};
Object.keys(tickerdata[filtKey])
.forEach((entry) => {
if(!!!(dst in currentBuffer[src])){
currentBuffer[src][dst] = {};
}
if(entry == 'last'){
currentBuffer[src][dst]['lastPrice'] = tickerdata[filtKey][entry];
}
});
});
res(currentBuffer);
});
},//... rest of the module exports
For reference, each call to return ticker endpoint returns data in the following format: Poloniex API. Look at returnTicker endpoint for example.
I am guessing that there is a logical error in the extraction function but, I am not sure where.

Answer 1

UPDATE
What about this code?
module.exports = {
extractData: (tickerdata, marker) =>
Object.keys(tickerdata)
.map(x => x.split('_'))
.filter(x => x && x[0] == (marker || 'BTC') && x[1])
.map(x => x[0] + '_' + x[1])
.map(x => [x, Object.keys(tickerdata[x])
.map(y => [y, tickerdata[x][y].lastPrice])]);
and usage:
const extracted = {
ETH_STR: {
BTC: {
lastPrice: 1
}
},
BTC_ETH: {
STR: {
lastPrice: 1
}
},
BTC_STR: {
STR: {
lastPrice: 1
},
ETH: {
lastPrice: 2
}, //...
}, //...
};
const result = extractData(extracted, 'BTC');
console.log(JSON.stringify(result));
with result
[["BTC_ETH",[["STR",1]]],["BTC_STR",[["STR",1],["ETH",2]]]]

Answer 2

I have tinkered around with my code and, finally was able to make it work. Besides adding more code for extracting data from the API response object, tickerdata, I have changed the promise to return instead of resolve. This ensured that the flow remains in proper sequence. I used a then clause on the promise to retrieve the extracted values (named buff). Here is the full working code:
`module.exports = {
extractData: (markers) => {
// extracts the data for all markers which, are a comma separated string of base currencies
return new Promise((res, rej) => {
markers = (!!!(markers) ? 'USDT,BTC' : markers)
polinst.returnTicker()
.then((tickerdata) => {
let buff = {};
markers.split(',').forEach((marker) => {
Object.keys(tickerdata)
.filter((key) => {
return key.startsWith(marker);
})
.forEach((fkey) => {
let c = fkey.split('_'),
src = c[0],
dst = c[1];
buff[src] = (!!!(buff[src]) ? {} : buff[src]);
buff[src][dst] = (!!!(buff[src][dst]) ? {} : buff[src][dst]);
Object.keys(tickerdata[fkey])
.forEach((k) => {
if(k == 'last'){
buff[src][dst]['lastPrice'] = tickerdata[fkey][k];
}
else if(k == 'quoteVolume'){
buff[src][dst]['volume'] = tickerdata[fkey][k];
}
else if(k == 'lowestAsk'){
buff[src][dst]['ask'] = tickerdata[fkey][k];
}
else if(k == 'highestBid'){
buff[src][dst]['highestBid'] = tickerdata[fkey][k];
}
});
});
});
return buff;
}).then((d)=>{
res(d);
}).catch((err)=>{
console.log(err);
});
});
},
};`