以下给大家举个小例子：
<!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>
    <script>
        function maxNum(a, b, c) {
        let temp = 0;
        if (b > a) {
            temp = b;//当b大于a时，把b的值赋给temp
            b = a;//再把a的值赋给b
            a = temp;//把temp从b那儿得来的值再赋给了a
        }
        if (c > a) {
            temp = c;//当c大于a时，把c的值赋给temp
            c = a;//再把a的值赋给c
            a = temp;//把temp从c那儿得来的值再赋给了a
        }
        document.write("最大值是" + a)//现在输出的最大值就是a了
    }
    maxNum(1,2,3)//输出最大值是3
    </script>
</body>
</html>

 

 希望能对大家有帮助！