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FrontEnd/JavaScript

두 날짜를 입력받아 남은 일수를 계산하는 JavaScript 코드

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SMALL

<!DOCTYPE html>
<html lang="ko">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>날짜 간 일수 계산기</title>
    <style>
        body {
            font-family: Arial, sans-serif;
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
            min-height: 100vh;
            background-color: #f4f4f4;
            margin: 0;
        }
        .container {
            background-color: #fff;
            padding: 30px;
            border-radius: 8px;
            box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
            text-align: center;
        }
        h1 {
            color: #333;
            margin-bottom: 20px;
        }
        .input-group {
            margin-bottom: 15px;
            text-align: left;
        }
        .input-group label {
            display: block;
            margin-bottom: 5px;
            color: #555;
            font-weight: bold;
        }
        .input-group input[type="date"] {
            width: calc(100% - 22px); /* Padding 고려 */
            padding: 10px;
            border: 1px solid #ccc;
            border-radius: 4px;
            font-size: 16px;
        }
        button {
            background-color: #007bff;
            color: white;
            padding: 12px 20px;
            border: none;
            border-radius: 5px;
            cursor: pointer;
            font-size: 18px;
            margin-top: 10px;
            transition: background-color 0.3s ease;
        }
        button:hover {
            background-color: #0056b3;
        }
        #result {
            margin-top: 25px;
            font-size: 20px;
            font-weight: bold;
            color: #333;
        }
    </style>
</head>
<body>
    <div class="container">
        <h1>날짜 간 일수 계산기</h1>
        <div class="input-group">
            <label for="startDate">시작 날짜:</label>
            <input type="date" id="startDate" value="2025-06-14"> </div>
        <div class="input-group">
            <label for="endDate">끝 날짜:</label>
            <input type="date" id="endDate" value="2025-12-25"> </div>
        <button onclick="calculateAndDisplayDays()">일수 계산</button>
        <p id="result"></p>
    </div>

    <script>
        /**
         * 두 날짜 문자열 사이의 일수를 계산하는 함수
         * @param {string} startDateString 'YYYY-MM-DD' 형식의 시작 날짜 문자열
         * @param {string} endDateString 'YYYY-MM-DD' 형식의 끝 날짜 문자열
         * @returns {number} 시작 날짜부터 끝 날짜까지의 일수. 유효하지 않은 날짜 또는 시작 날짜가 끝 날짜보다 늦을 경우 -1을 반환.
         */
        function calculateDaysBetweenDates(startDateString, endDateString) {
            const startDate = new Date(startDateString);
            const endDate = new Date(endDateString);

            // 시간을 자정으로 설정하여 날짜 계산의 정확성을 높입니다.
            startDate.setHours(0, 0, 0, 0);
            endDate.setHours(0, 0, 0, 0);

            // 유효성 검사
            if (isNaN(startDate.getTime()) || isNaN(endDate.getTime())) {
                console.error("유효하지 않은 날짜 형식입니다. 'YYYY-MM-DD' 형식을 사용해주세요.");
                return -1;
            }

            // 시작 날짜가 끝 날짜보다 늦은 경우 (또는 같은 날)
            if (startDate.getTime() > endDate.getTime()) {
                console.warn("시작 날짜가 끝 날짜보다 늦거나 같습니다.");
                // 같은 날의 경우 0일로 처리하고 싶으면 여기에 'return 0;' 추가
                return -1; // 또는 0을 반환할 수도 있습니다.
            }

            // 두 날짜 간의 시간 차이 (밀리초)를 계산합니다.
            const timeDifference = endDate.getTime() - startDate.getTime();

            // 밀리초를 일수로 변환합니다. (1일 = 24시간 * 60분 * 60초 * 1000밀리초)
            // Math.ceil을 사용하여 소수점 이하를 올림 처리하여, 하루가 채 안 되는 차이도 하루로 계산합니다.
            // 만약 시작일과 종료일이 같은 날이면 0을 반환하려면 Math.floor나 Math.round를 고려해야 합니다.
            // 여기서는 시작일 포함, 종료일 미포함 개념으로 일수를 계산하기 위해 Math.ceil을 사용합니다.
            // 예를 들어, 2025-01-01부터 2025-01-02는 1일
            const daysDifference = Math.ceil(timeDifference / (1000 * 60 * 60 * 24));

            return daysDifference;
        }

        // HTML 요소와 상호작용하는 함수
        function calculateAndDisplayDays() {
            const startDateInput = document.getElementById('startDate').value;
            const endDateInput = document.getElementById('endDate').value;
            const resultElement = document.getElementById('result');

            const days = calculateDaysBetweenDates(startDateInput, endDateInput);

            if (days === -1) {
                resultElement.textContent = "날짜를 올바르게 입력해주세요 (YYYY-MM-DD). 시작 날짜는 끝 날짜보다 이전이어야 합니다.";
                resultElement.style.color = "red";
            } else {
                resultElement.textContent = `두 날짜 사이에는 ${days}일 남았습니다.`;
                resultElement.style.color = "blue";
            }
        }
    </script>
</body>
</html>

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