Learn-JavaScript/14. Advanced Functions.html at main · Sandeep6135/Learn-JavaScript · GitHub

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<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>Modern Functional JS</title>
    <style>
        body {
            font-family: 'Segoe UI', system-ui, sans-serif;
            display: flex;
            justify-content: center;
            padding-top: 50px;
            background: #f8f9fa;
        }

        .card {
            background: white;
            padding: 2rem;
            border-radius: 12px;
            box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
            width: 350px;
        }

        input {
            width: 100%;
            padding: 10px;
            margin: 10px 0;
            border: 1px solid #ddd;
            border-radius: 6px;
            box-sizing: border-box;
        }

        button {
            width: 100%;
            padding: 10px;
            background: #007bff;
            color: white;
            border: none;
            border-radius: 6px;
            cursor: pointer;
            font-weight: bold;
        }

        button:hover {
            background: #0056b3;
        }

        #output {
            margin-top: 20px;
            font-size: 0.9rem;
            color: #333;
        }

        .result-row {
            display: flex;
            justify-content: space-between;
            border-bottom: 1px solid #eee;
            padding: 8px 0;
        }
    </style>
</head>

<body>

    <div class="card">
        <h3>Price Calculator</h3>
        <input id="priceInput" type="number" placeholder="Enter Base Price (£)">
        <button onclick="handleCalculation()">Run Pipeline</button>
        <div id="output"></div>
    </div>

    <script>
        /** * ADVANCED CONCEPTS USED:
         * 1. Arrow Functions (Concise syntax)
         * 2. Composition (Passing the result of one function to another)
         * 3. Template Literals (Cleaner string building)
         */

        // Pure Functions
        const applyDiscount = price => price * 0.9;
        const applyTax = price => price * 1.18;
        const format = val => `£${val.toFixed(2)}`;

        // The "Pipeline" - Composing the logic
        // This reads: format(applyTax(applyDiscount(input)))
        const getFinalPrice = (price) => format(applyTax(applyDiscount(price)));

        function handleCalculation() {
            const input = document.getElementById("priceInput");
            const display = document.getElementById("output");
            const val = parseFloat(input.value);

            if (isNaN(val) || val <= 0) {
                display.innerHTML = "<small style='color:red'>Please enter a valid amount.</small>";
                return;
            }

            // Using our composed function
            display.innerHTML = `
            <div class="result-row"><span>Original:</span> <b>${format(val)}</b></div>
            <div class="result-row"><span>Discounted:</span> <b>${format(applyDiscount(val))}</b></div>
            <div class="result-row"><span>Final (Inc. Tax):</span> <b style="color:green">${getFinalPrice(val)}</b></div>
        `;
        }
    </script>

</body>

</html>