函数在nodejs中完成所有计算之前返回值

Question

有时在计算某些项目之前返回总数。我试过了

if(i === receivedItems.length-1){
  return callback(total)
}

解决这个问题，但我没有运气。

function getItemPrices(offer, callback) {
  offer.getExchangeDetails((err, status, tradeInitTime, receivedItems, sentItems) => {
    if (err) {
      return callback(-1)
    } else {
      let total = 0
      for (let i = 0; i < receivedItems.length; i++) {
        let url = "http://steamcommunity.com/market/priceoverview/?currency=1&appid=" + receivedItems[i].appid + "&market_hash_name=" + receivedItems[i].market_hash_name + ""
        url = url.replace(/#/, "%23")
        request(url, function(error, response, body) {
          if (error) {
            console.log(error)
          }
          if (!error && response.statusCode == 200) {
            total += parseFloat(JSON.parse(body).lowest_price.replace(/\$/, ""))
            if (i === receivedItems.length - 1) {
              return callback(total)
            }
          }
        })
      }
    }
  })
}