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CSS

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JavaScript

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Babel includes JSX processing.

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HTML 

              
                <!DOCTYPE html>
<html lang="ja">
<head>
    <meta charset="UTF-8">
    <title>回文確認</title>
    <style type="text/css">
        body{ 
            background-color:#f0f8ff;
            color : #000000;
            margin-right: auto;
            margin-left : auto;
            width:700px;
            font-size:200%;
            font-weight: 900;
        }
    </style>
</head>
<body>
    <h1>回文確認</h1>
    <div>確認したい文字を入力してください</div>
    <input style="width: 75%;" type="text" id="check" placeholder="確認したい文字列">
    <input type="button" onClick="check()" value="確認する">
    <div>(入力した文字)</div>
    <span id='check_word''></span>

    <div>(反対にした文字)</div>
    <span style="color:red;" id='complete'></span>
    <br><br>
    <div id='check_result'></div>
</body>
<script type="text/javascript">
    function check(){
        var word = document.getElementById("check").value;

        if(word != ''){
            //入力した文字を表示
            document.getElementById('check_word').innerHTML = word;

            //入力された文字列を反対にする処理
            const converted = [];    // 文字を格納する配列を用意する。
            for (let i = 0, len = word.length; i < len; i++) {
            const char = word.charAt(i);    // インデックスの位置の一文字を取得する。
            converted.push(char);           //  要素を追加する。
            }
            let reversed = '';    // 反転された文字を入れる変数を用意する。
            for (let i = 0, len = converted.length; i < len; i++) {
            const popped = converted.pop();    // 配列の末尾から1つ取り出す。
            reversed += popped;                // 文字を繋げる。
            }

            //反対にした文字を表示
            document.getElementById('complete').innerHTML = reversed;

            //入力文字と反対文字が一致しているか確認して表示
            if(word == reversed){
                var check_result = '回文です';
            } else {
                var check_result = '回文ではないです';
            }
            document.getElementById('check_result').innerHTML = check_result;
        }
    }
</script>
</html>
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