Currency conversion

File: currency_conversion.html

<!DOCTYPE html>
<html>
<head>
  <title>math.js | currency conversion</title>

  <script src="http://cdnjs.cloudflare.com/ajax/libs/mathjs/3.9.3/math.min.js"></script>

  <style>
    body,
    html,
    input {
      font-size: 11pt;
      font-family: verdana, arial, sans-serif;
      color: #4d4d4d;
      max-width: 600px;
    }

    h1 {
      font-size: 120%;
    }

    input {
      padding: 5px;
      width: 400px;
    }
  </style>
</head>
<body>

<h1>Currency conversion with math.js</h1>

<p>
  This example demonstrates how you can fetch actual currencies from <a href="http://fixer.io">fixer.io</a> and use them in math.js.
</p>

<p id="info">
  fetching currencies...
</p>
<p>
  <label for="expr">Enter an expression with currencies:</label>
</p>
<div id="form" style="display: none;">
  <p>
    <input id="expr" value="5 EUR + 2 * 3 EUR in USD" /><br/>
  </p>
  <p id="result"></p>
</div>

<script>
  fetchAndImportCurrencies()
      .then(function (currencies) {
        document.getElementById('expr').oninput = evaluate;
        document.getElementById('form').style.display = '';
        document.getElementById('info').innerHTML = 'Available currencies: ' + currencies.join(', ');

        evaluate();
      })

  function fetchAndImportCurrencies () {
    // fetch actual currency conversion rates
    return fetch('https://api.fixer.io/latest')
        .then(function (response) {
          return response.json();
        }).then(function (data) {
          // import the currencies
          math.createUnit(data.base)
          Object.keys(data.rates).forEach(function (currency) {
            math.createUnit(currency, math.unit(1 / data.rates[currency], data.base));
          });

          // return an array with all available currencies
          return Object.keys(data.rates).concat(data.base);
        });
  }

  function evaluate () {
    var expr = document.getElementById('expr');
    var result = document.getElementById('result');

    try {
      var resultStr = math.format(math.eval(expr.value), {notation: 'fixed', precision: 2})
      result.innerHTML = '<span style="color: dodgerblue;">' + resultStr + '</span>';
    }
    catch (err) {
      result.innerHTML = '<span style="color: red;">' + err.toString() + '</span>';
    }
  }
</script>
</body>
</html>
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