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Build a Currency Converter in 10 Minutes with JavaScript

#api #javascript #tutorial #webdev

Ever needed to add currency conversion to your app? Whether you're building an e-commerce platform, a travel app, or a finance dashboard — you'll need reliable exchange rates.

In this tutorial, I'll show you how to build a working currency converter in under 10 minutes using vanilla JavaScript and the Currency Exchange Rates API on RapidAPI.

What We're Building

A simple web-based currency converter that:

  • Converts between 31 major currencies
  • Shows real-time rates from the European Central Bank (ECB)
  • Updates instantly when you change the amount or currency

Currency Converter Demo

Prerequisites

  • Basic JavaScript knowledge
  • A free RapidAPI account (sign up here)
  • A text editor and browser

Step 1: Get Your API Key (1 minute)

  1. Head to the Currency Exchange Rates API on RapidAPI
  2. Click Subscribe to Test and select the Free plan (100 requests/day — plenty for development)
  3. Copy your X-RapidAPI-Key from the code snippets section

Step 2: Build the HTML (3 minutes)

Create an index.html file:


html
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Currency Converter</title>
  <style>
    * { margin: 0; padding: 0; box-sizing: border-box; }
    body {
      font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
      display: flex; justify-content: center; align-items: center;
      min-height: 100vh; background: #f0f2f5;
    }
    .converter {
      background: white; padding: 2rem; border-radius: 12px;
      box-shadow: 0 2px 10px rgba(0,0,0,0.1); width: 400px;
    }
    h1 { font-size: 1.5rem; margin-bottom: 1.5rem; text-align: center; }
    .field { margin-bottom: 1rem; }
    label { display: block; font-size: 0.875rem; color: #666; margin-bottom: 4px; }
    input, select {
      width: 100%; padding: 10px 12px; border: 1px solid #ddd;
      border-radius: 8px; font-size: 1rem;
    }
    .result {
      text-align: center; padding: 1.5rem; background: #f8f9fa;
      border-radius: 8px; margin-top: 1rem;
    }
    .result .amount { font-size: 2rem; font-weight: 700; color: #2563eb; }
    .result .rate { font-size: 0.875rem; color: #666; margin-top: 4px; }
    .swap-btn {
      display: block; margin: 0.5rem auto; background: none;
      border: 1px solid #ddd; border-radius: 50%; width: 36px;
      height: 36px; cursor: pointer; font-size: 1.2rem;
    }
    .swap-btn:hover { background: #f0f2f5; }
  </style>
</head>
<body>
  <div class="converter">
    <h1>💱 Currency Converter</h1>
    <div class="field">
      <label>Amount</label>
      <input type="number" id="amount" value="100" min="0" step="0.01">
    </div>
    <div class="field">
      <label>From</label>
      <select id="fromCurrency"></select>
    </div>
    <button class="swap-btn" id="swap" title="Swap currencies">⇅</button>
    <div class="field">
      <label>To</label>
      <select id="toCurrency"></select>
    </div>
    <div class="result">
      <div class="amount" id="resultAmount">—</div>
      <div class="rate" id="resultRate"></div>
    </div>
  </div>
  <script src="app.js"></script>
</body>
</html>
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