javascript - 异步 JavaScript 和函数

Question

我正在编写 Steam 机器人来计算发送元素的价格。我无法正确使用函数。我想从 URL 获取价格，然后将其添加到 console.log。

我做不到，因为 console.log 在循环之前执行。

我对 Javascript 很陌生，我无法修复它:(

var whole_price = 0;
for(var i=0 ; i<offer.itemsToReceive.length; i++){
    getPrice(offer.itemsToReceive[i].market_hash_name, function(price){
        whole_price += price;
    }); 
}
console.log('Accepted offer from ' + offer.partner + ' with ' + offer.itemsToReceive.length + ' items valued as '+whole_price+'$.' );

获取 URL 价格的函数:

function getPrice(name, callback){
    name = name.replace(/\ +/g, '%20');
    var url = 'http://steamcommunity.com/market/priceoverview/?currency=1&appid=730&market_hash_name='+name;
    var price = 0;


    request(url ,function(error, res, body){
        var useCSGOBACKPACK = false;
        if(!error && res.statusCode == 200){
            body = JSON.parse(body);
            if(body.success == true){
                price = body.median_price.substr(1);
            }else{
                useCSGOBACKPACK = true;
            }
        }else{
            useCSGOBACKPACK = true;
        }

        if(useCSGOBACKPACK==true){
            url = 'http://csgobackpack.net/api/GetItemPrice/?id='+name+'&currency=USD';
            request(url, function(error, res, body){
                body = JSON.parse(body);
                price = body.median_price;
            });
        }

        callback(price);
    });

}

Answer 1

做这样的事情的最好方法是......

var whole_price = 0;
var requestsMade = 0;
for(var i=0 ; i<offer.itemsToReceive.length; i++){
    requestsMade++;
    getPrice(offer.itemsToReceive[i].market_hash_name, function(price){
        whole_price += price;
        requestsMade++;

        if(requestsMade == offer.itemsToReceive.length-1)
        {
            console.log(YOUR MESSAGE);
        }
    }); 
}

这基本上是确保在发出并响应所有请求之前不会记录消息。这是因为即使所有调用都是按特定顺序进行的，它们也可能以不同的顺序完成。