This tutorial walks you through creating an Exchange Rate Calculator. It's an excellent project for those looking to work with external APIs, manipulate the DOM, and handle events in JavaScript. You'll build a user interface allowing users to select currencies and input amounts and see the converted values based on real-time exchange rates fetched from an external API.

Project Specifications

UI Components: Two dropdown lists for selecting currencies and two input fields for entering the amount to be converted and displaying the converted amount.

Data Source: Fetch exchange rates from the ExchangeRate-API.

Dynamic Updates: Automatically update the displayed exchange rate and converted amount as the user types or selects different currencies.

Functionality: Include a feature to swap the currencies.

Development Steps

Project Setup

Create a directory named exchange-rate. Inside, create three files: index.html, style.css, and script.js.

Building the UI - index.html

Define the structure with HTML, including dropdown lists for currency selection and input fields for amounts. Incorporate a swap button to toggle between the selected currencies and display the current exchange rate.

Let's create index.html and add the following code to it:

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />
    <title>Exchange Rate Calculator</title>
    <link rel="stylesheet" href="style.css" />
  </head>
  <body>
    <img src="img/money.png" alt="" class="money-img" />
    <h1>Exchange Rate Calculator</h1>
    <p>Choose the currency and the amounts to get the exchange rate</p>

    <div class="container">
      <div class="currency">
        <select id="currency-one">
          <option value="AED">AED</option>
          <option value="ARS">ARS</option>
          <option value="AUD">AUD</option>
          <option value="BGN">BGN</option>
          <option value="BRL">BRL</option>
          <option value="BSD">BSD</option>
          <option value="CAD">CAD</option>
          <option value="CHF">CHF</option>
          <option value="CLP">CLP</option>
          <option value="CNY">CNY</option>
          <option value="COP">COP</option>
          <option value="CZK">CZK</option>
          <option value="DKK">DKK</option>
          <option value="DOP">DOP</option>
          <option value="EGP">EGP</option>
          <option value="EUR">EUR</option>
          <option value="FJD">FJD</option>
          <option value="GBP">GBP</option>
          <option value="GTQ">GTQ</option>
          <option value="HKD">HKD</option>
          <option value="HRK">HRK</option>
          <option value="HUF">HUF</option>
          <option value="IDR">IDR</option>
          <option value="ILS">ILS</option>
          <option value="INR">INR</option>
          <option value="ISK">ISK</option>
          <option value="JPY">JPY</option>
          <option value="KRW">KRW</option>
          <option value="KZT">KZT</option>
          <option value="MXN">MXN</option>
          <option value="MYR">MYR</option>
          <option value="NOK">NOK</option>
          <option value="NZD">NZD</option>
          <option value="PAB">PAB</option>
          <option value="PEN">PEN</option>
          <option value="PHP">PHP</option>
          <option value="PKR">PKR</option>
          <option value="PLN">PLN</option>
          <option value="PYG">PYG</option>
          <option value="RON">RON</option>
          <option value="RUB">RUB</option>
          <option value="SAR">SAR</option>
          <option value="SEK">SEK</option>
          <option value="SGD">SGD</option>
          <option value="THB">THB</option>
          <option value="TRY">TRY</option>
          <option value="TWD">TWD</option>
          <option value="UAH">UAH</option>
          <option value="USD" selected>USD</option>
          <option value="UYU">UYU</option>
          <option value="VND">VND</option>
          <option value="ZAR">ZAR</option>
        </select>
        <input type="number" id="amount-one" placeholder="0" value="1" />
      </div>

      <div class="swap-rate-container">
        <button class="btn" id="swap">
          Swap
        </button>
        <div class="rate" id="rate"></div>
      </div>

      <div class="currency">
        <select id="currency-two">
          <option value="AED">AED</option>
          <option value="ARS">ARS</option>
          <option value="AUD">AUD</option>
          <option value="BGN">BGN</option>
          <option value="BRL">BRL</option>
          <option value="BSD">BSD</option>
          <option value="CAD">CAD</option>
          <option value="CHF">CHF</option>
          <option value="CLP">CLP</option>
          <option value="CNY">CNY</option>
          <option value="COP">COP</option>
          <option value="CZK">CZK</option>
          <option value="DKK">DKK</option>
          <option value="DOP">DOP</option>
          <option value="EGP">EGP</option>
          <option value="EUR" selected>EUR</option>
          <option value="FJD">FJD</option>
          <option value="GBP">GBP</option>
          <option value="GTQ">GTQ</option>
          <option value="HKD">HKD</option>
          <option value="HRK">HRK</option>
          <option value="HUF">HUF</option>
          <option value="IDR">IDR</option>
          <option value="ILS">ILS</option>
          <option value="INR">INR</option>
          <option value="ISK">ISK</option>
          <option value="JPY">JPY</option>
          <option value="KRW">KRW</option>
          <option value="KZT">KZT</option>
          <option value="MXN">MXN</option>
          <option value="MYR">MYR</option>
          <option value="NOK">NOK</option>
          <option value="NZD">NZD</option>
          <option value="PAB">PAB</option>
          <option value="PEN">PEN</option>
          <option value="PHP">PHP</option>
          <option value="PKR">PKR</option>
          <option value="PLN">PLN</option>
          <option value="PYG">PYG</option>
          <option value="RON">RON</option>
          <option value="RUB">RUB</option>
          <option value="SAR">SAR</option>
          <option value="SEK">SEK</option>
          <option value="SGD">SGD</option>
          <option value="THB">THB</option>
          <option value="TRY">TRY</option>
          <option value="TWD">TWD</option>
          <option value="UAH">UAH</option>
          <option value="USD">USD</option>
          <option value="UYU">UYU</option>
          <option value="VND">VND</option>
          <option value="ZAR">ZAR</option>
        </select>
        <input type="number" id="amount-two" placeholder="0" />
      </div>
    </div>

    <script src="script.js"></script>
  </body>
</html>

Styling - style.css

Apply CSS to style the calculator, focusing on layout, typography, and form controls for a user-friendly interface. Ensure responsiveness so the calculator looks good on various devices.

Let's create a CSS file named style.css and add the following CSS code to it:

:root {
  --primary-color: #5fbaa7;
}

* {
  box-sizing: border-box;
}

body {
  background-color: #f4f4f4;
  font-family: Arial, Helvetica, sans-serif;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  height: 100vh;
  margin: 0;
  padding: 20px;
}

h1 {
  color: var(--primary-color);
}

p {
  text-align: center;
}

.btn {
  color: #fff;
  background: var(--primary-color);
  cursor: pointer;
  border-radius: 5px;
  font-size: 12px;
  padding: 5px 12px;
}

.money-img {
  width: 150px;
}

.currency {
  padding: 40px 0;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.currency select {
  padding: 10px 20px 10px 10px;
  -moz-appearance: none;
  -webkit-appearance: none;
  appearance: none;
  border: 1px solid #dedede;
  font-size: 16px;
  /*  You may not need these following lines. The arrow did not show for me on MacOS/Chrome so I added it. Just remove it if you would like  */
  background: transparent;
  background-image: url('data:image/svg+xml;charset=US-ASCII,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20width%3D%22292.4%22%20height%3D%22292.4%22%3E%3Cpath%20fill%3D%22%20000002%22%20d%3D%22M287%2069.4a17.6%2017.6%200%200%200-13-5.4H18.4c-5%200-9.3%201.8-12.9%205.4A17.6%2017.6%200%200%200%200%2082.2c0%205%201.8%209.3%205.4%2012.9l128%20127.9c3.6%203.6%207.8%205.4%2012.8%205.4s9.2-1.8%2012.8-5.4L287%2095c3.5-3.5%205.4-7.8%205.4-12.8%200-5-1.9-9.2-5.5-12.8z%22%2F%3E%3C%2Fsvg%3E');
  background-position: right 10px top 50%, 0, 0;
  background-size: 12px auto, 100%;
  background-repeat: no-repeat;
}

.currency input {
  border: 0;
  background: transparent;
  font-size: 30px;
  text-align: right;
}

.swap-rate-container {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.rate {
  color: var(--primary-color);
  font-size: 14px;
  padding: 0 10px;
}

select:focus,
input:focus,
button:focus {
  outline: 0;
}

@media (max-width: 600px) {
  .currency input {
    width: 200px;
  }
}

Adding Interactivity - script.js

Variables Initialization: Get references to UI elements (dropdowns, input fields, the swap button, and the rate display area).

Fetching Exchange Rates: Use the fetch API to retrieve current exchange rates based on the selected currency.

Calculating and Displaying Rates: Implement a function to calculate the conversion using the fetched rates and update the UI accordingly.

Swap Functionality: Add an event listener to the swap button to interchange the selected currencies and recalculate the displayed amount.

Let's create a JavaScript file named script.js and add the following JavaScript code to it:

const currencyEl_one = document.getElementById('currency-one');
const amountEl_one = document.getElementById('amount-one');
const currencyEl_two = document.getElementById('currency-two');
const amountEl_two = document.getElementById('amount-two');

const rateEl = document.getElementById('rate');
const swap = document.getElementById('swap');

// Fetch exchange rates and update the DOM
function calculate() {
  const currency_one = currencyEl_one.value;
  const currency_two = currencyEl_two.value;

  fetch(`https://api.exchangerate-api.com/v4/latest/${currency_one}`)
    .then(res => res.json())
    .then(data => {
      // console.log(data);
      const rate = data.rates[currency_two];

      rateEl.innerText = `1 ${currency_one} = ${rate} ${currency_two}`;

      amountEl_two.value = (amountEl_one.value * rate).toFixed(2);
    });
}

// Event listeners
currencyEl_one.addEventListener('change', calculate);
amountEl_one.addEventListener('input', calculate);
currencyEl_two.addEventListener('change', calculate);
amountEl_two.addEventListener('input', calculate);

swap.addEventListener('click', () => {
  const temp = currencyEl_one.value;
  currencyEl_one.value = currencyEl_two.value;
  currencyEl_two.value = temp;
  calculate();
});

calculate();

JavaScript Code Explanation:

Fetching and Displaying Exchange Rates: The calculate function is the core of this application. It fetches the current exchange rate for the selected currency pair and updates the DOM to display the conversion rate and the calculated amount in the second currency.

Event Listeners for Real-time Updates: By adding event listeners to the currency selection dropdowns and input fields, the application reacts to user input, instantly recalculating and displaying the converted amount without needing to press a submit button.

Swap Functionality: The swap feature is implemented by simply exchanging the values of the currency selection dropdowns and recalculating the conversion, enhancing user experience by providing a quick way to reverse the conversion direction.

Open index.html in Browser

Let's open the index.html file in the browser, and you will be able to see the following screen:

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Exchange Rate Calculator Project with JavaScript, HTML and CSS