JavaScript 中的货币转换器

Question

我正在努力完成这个练习：

1. 询问用户有多少钱。

2. 接下来，询问他们有什么货币

3. 最后，询问他们想要将其转换成什么

4. 将货币转换为所需的输出

5. 打印一条带有其他货币价值的漂亮警报消息

6. 您的代码必须至少使用两个函数。

7. 一个函数应该计算转换。

8. 一个函数应打印带有转换后的货币和货币名称的警报消息。

提示 - 使用两个转换函数可能是有意义的。一 函数可将任何货币转换为美元，并可将另一种货币转换为美元 从美元兑换成任何其他货币。

这是我的代码：

当我在浏览器中运行代码时，没有任何反应。 如果我正确计算转换并且当我运行此命令时什么也没有打印出来，我就不是真的。

我解决了问题，所以它现在正在运行，但我仍然没有得到函数转换部分

'use strict';
let money = Number(prompt("How much money do you have?."));
let moneyCurrency = prompt("What currency are you using?.");
let currencysys = prompt("What currency do you want to convert it to? EUR, JPY, GBP, USD, or  BRL");


function convertCurrency(currency, currencySystem) {
  if (currencySystem === 'JPY' || currencySystem === 'jpy') {
    return convertJPYtoUSD(currency);
  } 
  else if (currencySystem  === 'Eur' || currencySystem  === 'eur') {
    return convertEurtoUSD(currency);
  }  
  else if (currencySystem  === 'GBP'|| currencySystem  === 'gbp') {
    return convertGBPtoUSD(currency);
  }
  else if ( currencySystem  === 'BRL'|| currencySystem  === 'brl') {
    return convertBRLtoUSD(currency);
  }
}

function convertJPYtoUSD(JPY) {
  return  (JPY * 0.91);
}

function printCurrencyMessage(convertedCurrency, currencysys,round) {
  if (round === undefined || isNaN(Number(round))) {
    round = 0;
  }
}

console.log("The converted currency is "+currencySystem + ".");

我遇到了一些麻烦，数学代码不正确 100GBP 兑换 JPY 应该是 19,103.08，但我得到了完全不同的东西

'use strict';
let money = Number(prompt("How much money do you have?."));
let moneyCurrency = prompt("What currency are you using?.");
let currencysys = prompt("What currency do you want to convert it to? EUR, JPY, GBP, USD, or  BRL");



let currentExchange = {
  "USD": 1,
  "EURO": 0.91,
  "JPY": 124.17,
  "GBP": 0.65,
  "BRL": 3.51,
}

let currentExchanges = currentExchange[currency];

function convertCurrency(currencyNeeded, moneyAmount) {
  let exchange_value = moneyAmount * exchange_factor
  return exchange_value
}

function convertCurrency(currencyNeeded, moneyAmount) {
  let exchange_factor = currentExchange[currencyNeeded];
  let exchange_value = moneyAmount / exchange_factor
  let value = moneyAmount * exchange_factor
  console.log("The converted amount is $ " + (exchange_value.toFixed(2)) + "in " + currencyNeeded + ".");

  return exchange_value
};

convertCurrency(currencyNeeded, moneyAmount);

Answer 1

TDLR；

您正在尝试警告未定义的变量。

我建议你让你的函数为你返回你的值。比如：

console.log("The converted currency is "+ convertToCurrency(moneyCurrency, currencysys + ".");

解释和深入挖掘

您的签名

function convertCurrency(currency, currencySystem) {...

创建一个局部变量“currencySystem”，不能在函数作用域之外引用该变量。因此，currencySystem 是该函数的局部变量。

一些通用代码/架构建议：

使变量名称更有意义且一致。

使用所有货币兑换比率创建一个哈希图/对象，并使用单个函数进行数学转换。即：

var currencies = {
    usd: {
        conversion: 1,
    },
    eur: {
        conversion: .89
    },
    ...
};

function convertCurrency(fromCurrency, toCurrency, amount) {

    // ... not the best at thinking of the algorithm. Suggestions?
    // perhaps normalize fromCurrency to the dollar, then convert to toCurrency since I believe the dollar is the base/universal currency
};

var convertedCurrency = convertCurrency("USD", "EUR", 20.50);

alert("The converted amount is" + convertedCurrency);

如果您需要多个功能作为要求，那么拆分为每种货币转换并不是一个可怕的想法，但似乎有点太多的开销。

这是最终的工作解决方案：

'use strict';
let amount = Number(prompt("How much money do you have?."));
let currentCurrency = prompt("What currency are you using?");
let desiredCurrency = prompt("What currency do you want to convert it to? EUR, JPY, GBP, USD, or  BRL");

var currencyRates = {
    "USD": 1,
  "EUR": .8,
  "JPY": .7,
  "XXX": 5
};

function convertCurrency(currentCurrency, desiredCurrency, amount) {
  var currentRate = currencyRates[currentCurrency];
  var desiredRate = currencyRates[desiredCurrency];

  var USDAmount = amount * currentRate;
  var convertedAmount = USDAmount / desiredRate;

  return convertedAmount; // I think this is the right algorithm :/
}



var convertedCurrencyAmount = convertCurrency(currentCurrency, desiredCurrency, amount);

alert ("Converted: " + convertedCurrencyAmount);