JavaScript-Math内置对象

向下取整

Math.floor()：向下取整直接砍掉所有的小数位就是向下取整：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Demo</title>
    <script>
        let num = 3.9;
        let value = Math.floor(num);
        console.log(value);
    </script>
</head>
<body>
</body>
</html>

向上取整

Math.ceil()：向上取整只要有小数位就会给整数位 +1，然后砍掉所有小数位：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Demo</title>
    <script>
        let num = 3.9;
        let value = Math.ceil(num);
        console.log(value);
    </script>
</head>
<body>
</body>
</html>

四舍五入

Math.round()：四舍五入和小学数学一样，如果小数位满 5 就会进 1：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Demo</title>
    <script>
        let num = 3.5;
        let value = Math.round(num);
        console.log(value);
    </script>
</head>
<body>
</body>
</html>

绝对值

Math.abs()：和小学数学一样，统一变为正数：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Demo</title>
    <script>
        let num = -3;
        let value = Math.abs(num);
        console.log(value);
    </script>
</head>
<body>
</body>
</html>

生成随机数

Math.random()：生成随机数，会生成一个 0~1 的随机数，但是不包括1：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Demo</title>
    <script>
        let value = Math.random();
        console.log(value);
    </script>
</head>
<body>
</body>
</html>

需求：要求生成一个 1~10 的随机数：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Demo</title>
    <script>
        function getRandomIntInclusive(min, max) {
            min = Math.ceil(min);
            max = Math.floor(max);
            // 含最大值，含最小值
            return Math.floor(Math.random() * (max - min + 1)) + min;
        }

        let value = getRandomIntInclusive(1, 10);
        console.log(value);
    </script>
</head>
<body>
</body>
</html>

End