如何从javascript中的异步函数传递参数？ [复制]

Question

我正在尝试将两个值从两个异步函数传递给一个函数，但我不确定如何继续。代码如下：

    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)

我知道问题是我在异步函数之外调用函数，所以它没有收到数字，它给了我一个 NAN（不是数字），但我不知道如何正确传递这些两个参数分别在不同的函数中检索，是否可以将 btcPriceInUSD 和 priceExchangeMXN 合二为一并从那里调用？

提前致谢！

Answer 1

尝试使用$.when()，.then()，用完整函数的返回值代替异步函数范围之外的声明变量；还添加了一个错误处理程序

$.when($.getJSON(btcLink, function(btcData) {   
        return btcData.USD.last
       })     
, $.getJSON(exchangeRateLink, function(exchangeData) {   
        return exchangeData.query.results.rate.Rate
    }))
.then(convertToMXN, function err() {console.log(arguments)})

Answer 2

试试这个（简单地链接 ajax 调用，最后在两个值都可用时调用该方法）

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);
}