json - How to pass parameters from async function in javascript?

I am trying to pass two values to a function from two async functions and I am not sure how to proceed. Here is the code:

    var btcPriceInUSD;
var priceExchangeMXN;

var btcLink = "https://blockchain.info/ticker";
var exchangeRateLink = "http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20yahoo.finance.xchange%20where%20pair%20in%20%28%22USDMXN%22%29&env=store://datatables.org/alltableswithkeys&format=json";

//Get btc price in USD
$.getJSON(btcLink, function(btcData) 
    {   
        btcPriceInUSD = btcData.USD.last;
        //document.write(btcPriceInUSD);
    });     



//Get current USD/MXN exchange rate
$.getJSON(exchangeRateLink, function(exchangeData) 
    {   
        priceExchangeMXN = exchangeData.query.results.rate.Rate;
        //document.write(priceExchangeMXN);
    });     


//Convert btc price to MXN

function convertToMXN(btc,toMXN){
    var result = parseFloat(btc) * parseFloat(toMXN);
    document.write(result);
}


convertToMXN(btcPriceInUSD,priceExchangeMXN)

I know the issue is that I am calling the function outside of the async ones so it is not recieving the numbers and it is giving me a NAN (not a number) but I don't know how I would correctly pass those two parameters that are each retrieved in different functions, is it possible to combine the btcPriceInUSD and priceExchangeMXN in one and call it from there?

Thanks in advance!

Answer

try this (simply chaining the ajax calls and finally calling the method when both values are available)

var btcPriceInUSD;
var priceExchangeMXN;
var btcLink = "https://blockchain.info/ticker";
var exchangeRateLink = "http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20yahoo.finance.xchange%20where%20pair%20in%20%28%22USDMXN%22%29&env=store://datatables.org/alltableswithkeys&format=json";


//Get btc price in USD
$.getJSON(btcLink, function(btcData) 
    {   
        btcPriceInUSD = btcData.USD.last;
        //document.write(btcPriceInUSD);

      //Get current USD/MXN exchange rate
      $.getJSON(exchangeRateLink, function(exchangeData) 
        {   
           priceExchangeMXN = exchangeData.query.results.rate.Rate;

            //document.write(priceExchangeMXN);
           convertToMXN(btcPriceInUSD,priceExchangeMXN);
        });  

    });     

//Convert btc price to MXN
function convertToMXN(btc,toMXN){
    var result = parseFloat(btc) * parseFloat(toMXN);
    document.write(result);

}