How to return a nodejs callback as a number, from a JSON object property value?

Question

I am trying to do maths on a number within a JSON object (the price of a stock ticker).

I want it to be a variable called 'btcusd_price', that I can then use to do arithmetic with.

How do I get a variable i can work with?

var Bitfinex = require('bitfinex');

var bitfinex = new Bitfinex('your_key', 'your_secret');

var btcusd_price;

btcusd_price = bitfinex.ticker("btcusd", function(err, data) {
  if(err) {
    console.log('Error');
    return;
  }
  console.log(data.last_price);
  return data.last_price;
});

typeof btcusd_price;
console.log(btcusd_price); //i'm trying to work with the price, but it seems to be 'undefined'?

Looks like this famous dup http://stackoverflow.com/questions/14220321/how-do-i-return-the-response-from-an-asynchronous-call — elclanrs, Jun 14 '16 at 17:29
What do you mean by ` I can then use to do arithmetic with` - you want to reuse same object reference? — Medet Tleukabiluly, Jun 14 '16 at 17:56
I want to use the btc price as a variable in calculations later on (to calculate position sizes, for example). — fintech_novice, Jun 14 '16 at 22:16

score 0 · Answer 1 · answered Jun 14 '16 at 18:10

0

You have to set the values when they are available, the code is async and you were using the value before it is applied to btcusd_price. Note that the proper way to use the variable is when the callback executes its code.

Please, see the working code below:

Bitfinex = require('bitfinex');

var bitfinex = new Bitfinex('your_key', 'your_secret');

var btcusd_price;

bitfinex.ticker("btcusd", function(err, data) {
  if(err) {
    console.log('Error');
    return;
  }

  btcusd_price = data.last_price;
  console.log(typeof btcusd_price);
  console.log(btcusd_price);
});

answered Jun 14 '16 at 18:10

bpinhosilva

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How am I supposed to re-use the btc_price, outside of the function? – fintech_novice Jun 14 '16 at 22:28
Whenever you want as long as you wait the callback to fill in the value. If it's the case, use events. – bpinhosilva Jun 14 '16 at 23:27

How to return a nodejs callback as a number, from a JSON object property value?

1 Answers1