【JavaScript】逻辑运算符--非布尔值的与或运算、赋值运算符-CSDN博客

本文链接：https://blog.csdn.net/hefaxiang/article/details/147539730

1、逻辑运算符--非布尔值的与或运算

对于非布尔值进行与或运算，会先将其转换为布尔值，然后再运算，并且返回原值

（1）&&

如果&&的左右操作数转换为布尔值后都为true，则返回右操作数

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        var res1 = 1 && 2;
        var res2 = 2 && 1;
        document.writeln("res1=" + res1);
        document.writeln("<br>");
        document.writeln("res2=" + res2);

    </script>
</head>

<body>
</body>

</html>

结果：

如果两个值中有false，则返回靠前的false

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        var res1 = 0 && 2;
        var res2 = 1 && 0;
        document.writeln("res1=" + res1);
        document.writeln("<br>");
        document.writeln("res2=" + res2);

    </script>
</head>

<body>
</body>

</html>

结果：

总结：如果左操作数为true,则必然返回第二个值；如果第一个值为false，则必然返回第一个值。

（2）||

如果第一个值为true，则直接返回第一个值

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        var res1 = 1 || 2;
        var res2 = 2 || 1;
        document.writeln("res1=" + res1);
        document.writeln("<br>");
        document.writeln("res2=" + res2);

    </script>
</head>

<body>
</body>

</html>

结果：

如果第一个值为false，则直接返回第二个值

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        var res1 = 0 || 2;
        var res2 = 0 || 1;
        document.writeln("res1=" + res1);
        document.writeln("<br>");
        document.writeln("res2=" + res2);

    </script>
</head>

<body>
</body>

</html>

结果：

总结：如果第一个值为true，则直接返回第一个值；如果第一个值为alse返回，则直接第二个值。

2、赋值运算符

赋值运算符:可以将符号右侧的值赋值给符号左侧的变量。

（1）=

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        var res = 12;//将12赋值给res
        document.writeln(res);

    </script>
</head>

<body>
</body>

</html>

结果：

（2）+=

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        var res = 12;
        res += 5;//与res=res+5等价
        document.writeln(res);

    </script>
</head>

<body>
</body>

</html>

结果：

（3）-=

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        var res = 12;
        res -= 5;//与res=res-5等价
        document.writeln(res);

    </script>
</head>

<body>
</body>

</html>

结果：

（4）*=

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        var res = 12;
        res *= 5;//与res=res*5等价
        document.writeln(res);

    </script>
</head>

<body>
</body>

</html>

结果：

（5）/=

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        var res = 12;
        res /= 5;//与res=res/5等价
        document.writeln(res);

    </script>
</head>

<body>
</body>

</html>

结果：

（6）%=

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        var res = 12;
        res %= 5;//与res=res%5等价
        document.writeln(res);

    </script>
</head>

<body>
</body>

</html>

结果：