JavaScript函數返回NaN

Question

我有一個函數，它應該返回一個數字，但它返回NaN。 這是代碼

function priceCalc(cust, transit, passType){

    var price = 0;
    if (passType === "monthly"){
      if (cust === "student" || cust === "elderly"){
        price = transit.monthly / 2;
      } else if (cust === "transit worker"){
        price = 0;
      } else {
        price = transit.monthly;
      }

    } else if (passType === "pre paid"){
      if (cust === "transit worker") {
        price = Infinity;
      } else {
        value = prompt('How much would you like on your pass?');
        price = parseInt(value);
      }

    }
    return price;

  };

price是返回時應該有一個數值的變量，例如當我傳入學生為cust param，公共汽車為過境參數（每月屬性為60），並且每月傳遞一次鍵入param它應該返回30，但我得到NaN。 我正在對它進行茉莉花測試

describe('the application', function(){
  describe('publicPrice function', function(){

    it('takes in customer status, transit choice, and pass choice to calculate a price', function(){
      expect(App.priceCalc('adult', 'commuter rail', 'monthly')).toBe(80);
      expect(App.priceCalc('student', 'commuter rail', 'monthly')).toBe(40);
      expect(App.priceCalc('elderly', 'subway', 'monthly')).toBe(35);
      expect(App.priceCalc('transit worker', 'bus', 'monthly')).toBe(0);
    });
  });

});

如果重要的話，該功能是該模塊的一部分

var App = (function(){
  var Transport = function(mode, monthly, prepaid){
    this.mode = mode;
    this.monthly = monthly;
    this.prepaid = prepaid;
  };

  var commuterRail = new Transport('commuter rail', 80, 5);
  var bus = new Transport('bus', 60, 2);
  var subway = new Transport('subway', 70, 3);

  var customerStatus = prompt('Please enter your status. \nAdult \nElderly \nStudent \nTransit worker');
  var transitInput = prompt('Please select your method of transport: \ncommuter rail \nbus \nsubway');
  var passSelection = prompt('Please select a pass: \nMonthly \nPrepaid');

  var transitMethod;

  if(transitInput === "commuter rail"){
    transitMethod = commuterRail;
  } else if(transitInput === "bus"){
    transitMethod = bus;
  } else if (transitInput === "subway"){
    transitMethod = subway;
  }

  console.log(transitMethod);

  function priceCalc(cust, transit, passType){

    var price = 0;
    if (passType === "monthly"){
      if (cust === "student" || cust === "elderly"){
        price = transit.monthly / 2;
      } else if (cust === "transit worker"){
        price = 0;
      } else {
        price = transit.monthly;
      }

    } else if (passType === "pre paid"){
      if (cust === "transit worker") {
        price = Infinity;
      } else {
        value = prompt('How much would you like on your pass?');
        price = parseInt(value);
      }

    }
    return price;

  };

  var publicPrice = function(customerStatus, transitMethod, passSelection){
    return priceCalc(customerStatus, transitMethod, passSelection);
  };

  priceCalc(customerStatus, transitMethod, passSelection);

  return {
    // publicPrice: publicPrice,
    priceCalc: priceCalc
  };

})();

Answer 1

price = transit.monthly / 2;

在這里，您告訴解釋器monthly使用對象transit屬性。 在你的代碼transit是一個字符串， transit.monthly評估為undefined

undefined / 2計算為NaN

我認為你的意思是傳入你創建的變量對象而不是字符串。

Answer 2

transit.monthly可能是一個String，你應該在對它進行微積分之前解析它：

function priceCalc(cust, transit, passType){

var price = 0;
if (passType === "monthly"){
  if (typeof transit.monthly === 'string') {
    transit.monthly = Number(transit.monthly);
  }
  if (cust === "student" || cust === "elderly"){
    price = transit.monthly / 2;
  } else if (cust === "transit worker"){
    price = 0;
  } else {
    price = transit.monthly;
  }

} else if (passType === "pre paid"){
  if (cust === "transit worker") {
    price = Infinity;
  } else {
    value = prompt('How much would you like on your pass?');
    price = parseInt(value);
  }

}
return price;

};

Answer 3

您的函數需要三個參數：

function priceCalc(cust, transit, passType){}

在您的測試中，您傳遞一個字符串作為第二個參數transit ，但該函數被編寫為傳輸是一個對象。 所以當你做priceCalc函數時：

price = transit.monthly / 2

價格設置為NaN

在我看來，priceCalc函數需要一個Transport對象。

Answer 4

你將一個字符串傳遞給傳輸，你可能想傳遞一個類Transport的對象。

如果您添加此代碼（您的代碼）：

if(transit === "commuter rail"){
    transit = commuterRail;
  } else if(transit === "bus"){
    transit = bus;
  } else if (transit === "subway"){
    transit = subway;
  }

到你的功能開始，它可能會工作。

Answer 5

您需要將轉換方法名稱轉換為相應對象的代碼放入priceCalc函數中：

  function priceCalc(cust, transit, passType){

    var price = 0;
    if(transit === "commuter rail"){
        transit = commuterRail;
    } else if(transit === "bus"){
        transit = bus;
    } else if (transit === "subway"){
        transit = subway;
    }

    if (passType === "monthly"){
      if (cust === "student" || cust === "elderly"){
        price = transit.monthly / 2;
      } else if (cust === "transit worker"){
        price = 0;
      } else {
        price = transit.monthly;
      }

    } else if (passType === "pre paid"){
      if (cust === "transit worker") {
        price = Infinity;
      } else {
        value = prompt('How much would you like on your pass?');
        price = parseInt(value);
      }

    }
    return price;

  };

您當前使用transitInput變量執行此操作的transitInput是無用的，因為該變量沒有值。

Answer 6

你得到NaN，因為你試圖將“通勤鐵路”划分為2。

App.priceCalc('student', 'commuter rail', 'monthly') - > price = transit.monthly / 2; transit是“通勤鐵路” 。 您應該使用具有月度屬性的對象。