关于简易计算器通过innerHTML显示


<!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>简易计算器</title>
</head>

<body>
    <input type="text" value="">
    <select>
        <option>+</option>
        <option>-</option>
        <option>*</option>
        <option>/</option>
    </select>
    <input type="text">
    <button>计算</button>
    <span></span>
</body>
<script>
    var num1 = document.getElementsByTagName('input')[0]
    var num2 = document.getElementsByTagName('input')[1]
    var sec = document.getElementsByTagName('select')[0]
    var btn = document.getElementsByTagName('button')[0]
    var span = document.getElementsByTagName('span')[0]
    span.innerHTML = '计算啊'
    // console.log(span);

    btn.onclick = function () {
        var x = Number(num1.value)
        var y = Number(num2.value)
        if (x == '' || y == '') {
            span.innerHTML = '请检查输入是否完整'
        } else if (isNaN(x) || isNaN(y)) {
            span.innerHTML = '请检查输入是否为数字类型'
        } else {
            switch (sec.value) {
                case '+':
                    span.innerHTML = '计算结果为' + (x + y)
                    break;
                case '-':
                    span.innerHTML = '计算结果为' + (x - y)
                    break;
                case '*':
                    span.innerHTML = '计算结果为' + (x * y)
                    break;
                case '/':
                    span.innerHTML = '计算结果为' + (x / y)
                    break
            }
        }
    }


</script>

</html>