Javascript：货币转换器

Question

我是 javascript 新手，我正在尝试制作一个简单的货币转换器，当我选择 "£Pound" "£Pound" 或 "£Pound" "R$Real" 但当我选择 "R $Real" "R$Real" 运行 "Pound" "R$Real" 计算。

我花了几个小时试图弄清楚这一点（非常令人沮丧）。

如何解决？还有另一种方法吗？ （也尝试使用“ if ”和“ else if ”同样的问题）。谢谢！

这是 HTML：

<label>Amount:</label>
<input type="text" id="amount" />
<label>From:</label>
<select id="select1">
    <option value="pound">&pound; Pound</option>
    <option value="real">R$ Real</option>
</select>
<label>To:</label>
<select id="select2">
    <option value="pound">&pound; Pound</option>
    <option value="real">R$ Real</option>
</select>
<input type="button" onClick="calculation()" value="calculate" />
<div id="result"></div>

这是 JS：

function calculation() {
var amount = document.getElementById('amount').value;
var currency1 = document.getElementById('select1').value;
var currency2 = document.getElementById('select2').value;

switch((currency1)&&(currency2)){
    case "pound":
    case "pound":
        var y = amount * 1;
        document.getElementById('result').innerHTML = "£ " + parseFloat(Math.round(y * 100) / 100).toFixed(2);
        break
    case "pound":
    case "real":
        var x = currency2 = 3.40;
        var y = amount * x;
        document.getElementById('result').innerHTML = "R$ " + parseFloat(Math.round(y * 100) / 100).toFixed(2);
        break
    case "real":
    case "real":
        var y = amount * 1;
        document.getElementById('result').innerHTML = "R$ " + parseFloat(Math.round(y * 100) / 100).toFixed(2);
        break
    case "real":
    case "pound":
        var x = currency2 = 3.40;
        var y = amount / x;
        document.getElementById('result').innerHTML = "£ " + parseFloat(Math.round(y * 100) / 100).toFixed(2);
}}

Answer 1

要修复您的 JS，请执行以下操作：

问题是您的 switch 将计算为单个字符串，并且您使用的是贯穿 switch 语句 jsFiddle to demonstrate what I mean。

Switch Statement Documentation for JavaScript

function calculation() {
    var amount = document.getElementById('amount').value;
    var currency1 = document.getElementById('select1').value;
    var currency2 = document.getElementById('select2').value;

    switch (currency1 + ' ' + currency2) {
        case "pound pound":
            var y = amount * 1;
            document.getElementById('result').innerHTML = "£ " + parseFloat(Math.round(y * 100) / 100).toFixed(2);
            break
        case "pound real":
            var x = currency2 = 3.40;
            var y = amount * x;
            document.getElementById('result').innerHTML = "R$ " + parseFloat(Math.round(y * 100) / 100).toFixed(2);
            break
        case "real real":
            var y = amount * 1;
            document.getElementById('result').innerHTML = "R$ " + parseFloat(Math.round(y * 100) / 100).toFixed(2);
            break
        case "real pound":
            var x = currency2 = 3.40;
            var y = amount / x;
            document.getElementById('result').innerHTML = "£ " + parseFloat(Math.round(y * 100) / 100).toFixed(2);
    }
}

使用下面显示数字，然后将符号放在前面，因为此代码将在正确的位置添加逗号和分隔符，包括否定。

将数字格式化为货币：

function formatCurrency(num, precision) {
  //identify '(123)' as a negative number
  if (typeof num == 'string' && num.toString().indexOf('\\(') >= 0) {
    num = '-' + num;
  }

  if (num === '' || (num === '-' && precision === -1)) {
    return;
  }

  // if the number is valid use it, otherwise clean it
  if (isNaN(num)) {
    // clean number
    if (num === '' || (num === '-' && precision === -1)) {
      return;
    }

    if (isNaN(num)) {
      num = '0';
    }
  }

  // evalutate number input
  var numParts = String(num).split('.');
  var isPositive = (num == Math.abs(num));
  var hasDecimals = (numParts.length > 1);
  var decimals = (hasDecimals ? numParts[1].toString() : '0');
  var originalDecimals = decimals;

  // format number
  num = Math.abs(numParts[0]);
  num = isNaN(num) ? 0 : num;
  if (precision >= 0) {
    decimals = parseFloat('1.' + decimals); // prepend "0."; (IE does NOT round 0.50.toFixed(0) up, but (1+0.50).toFixed(0)-1
    decimals = decimals.toFixed(precision); // round
    if (decimals.substring(0, 1) == '2') {
      num = Number(num) + 1;
    }
    decimals = decimals.substring(2); // remove "0."
  }
  num = String(num);

  for (var i = 0; i < Math.floor((num.length - (1 + i)) / 3); i++) {
    num = num.substring(0, num.length - (4 * i + 3)) + ',' + num.substring(num.length - (4 * i + 3));
  }

  if ((hasDecimals && precision == -1) || precision > 0) {
    num += '.' + decimals;
  }

  // format symbol/negative
  var format = isPositive ? '%s%n' : '(%s%n)';
  var money = format.replace(/%s/g, '$');
  money = money.replace(/%n/g, num);
  return money;
}

console.log(formatCurrency(12002031203120, 2))