11.else-if-button.html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <input type="number" id="inp" />
    <button onclick="func()">Click!</button>
    <p id="info"></p>
    <script>
        const inp = document.querySelector('#inp');
        function func() {
            const pandamicCase = +inp.value;
            let r;
            if (pandamicCase >= 15000) {
                r = "疫情極為嚴重";
            } else if (pandamicCase >= 10000) {
                r = '疫情嚴重';
            } else if (pandamicCase >= 5000) {
                r = '疫情中等嚴重';
            } else if (pandamicCase >= 500) {
                r = '疫情開始增加';
            } else if (pandamicCase >= 100) {
                r = '疫情輕微';
            } else if (pandamicCase >= 10) {
                r = "無疫情";
            } else {
                r = '數字不合理';
            }
            info.innerText = r
        }
    </script>
</body>

</html>