JavaScript-其它数据类型转换为布尔类型

将 String 类型转换为布尔类型

只要字符串中有内容都会转换为 true, 只有字符串中没有内容才会转换为 false

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Demo</title>
    <script>
        let strOne = "abc";
        let strTwo = "";

        console.log(Boolean(strOne));
        console.log(Boolean(strTwo));

        console.log(typeof Boolean(strTwo));
        console.log(typeof Boolean(strTwo));
    </script>
</head>
<body>
</body>
</html>

将 Number 类型转换为布尔类型

只有数值是 0 才会转换为 false, 其它的都会转换为 true，如果是 NaN 也会转换为 false

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Demo</title>
    <script>
        let numOne = 999;
        let numTwo = -123;
        let numThree = -0;
        let numFour = 0;

        let flagOne = Boolean(numOne);
        let flagTwo = Boolean(numTwo);
        let flagThree = Boolean(numThree);
        let flagFour = Boolean(numFour);

        console.log(flagOne);
        console.log(typeof flagOne);

        console.log(flagTwo);
        console.log(typeof flagTwo);

        console.log(flagThree);
        console.log(typeof flagThree);

        console.log(flagFour);
        console.log(typeof flagFour);
    </script>
</head>
<body>
</body>
</html>

将 undefined 类型转换为布尔类型

undefined 会转换为 false

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Demo</title>
    <script>
        let value = undefined;

        let flag = Boolean(value);

        console.log(flag);
        console.log(typeof flag);
    </script>
</head>
<body>
</body>
</html>

将 null 类型转换为布尔类型

null 会转换为 false，空字符串 / 0 / NaN / undefined / null 会转换成 false, 其它的都是 true

在 JavaScript 中如果想将基本数据类型转换为布尔类型, 那么只需要调用 Boolean(常量 or 变量) 即可转换

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Demo</title>
    <script>
        let value = null;

        let flag = Boolean(value);

        console.log(flag);
        console.log(typeof flag);
    </script>
</head>
<body>
</body>
</html>

注意点：在 JavaScript 中 NaN 属于 Number 类型

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Demo</title>
    <script>
        let num = NaN;

        console.log(num);
        console.log(typeof num);

        let flag = Boolean(num);

        console.log(flag);
        console.log(typeof flag);
    </script>
</head>
<body>
</body>
</html>

posted @ 2021-03-25 10:21  BNTang  阅读(11)  评论(0)    收藏  举报