JavaScript 条件分支语句if...else

news2024/9/21 20:44:01

if 语句

只有当指定条件为 true 时，该语句才会执行代码

<!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>
        var sum = 300
        var youhuisum 
        if(sum>200){
            youhuisum = sum - 10
        }
        console.log(sum,youhuisum)
    </script>
</body>
</html>

if else语句

<!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>
        var sum = 150
        var youhuisum 
        if(sum>200){
            youhuisum = sum - 10
        }else{
            youhuisum = sum
        }
        console.log(sum,youhuisum)
    </script>
</body>
</html>

if...else if...else if语句

后面可以无限跟else if

总金额sum是100.

如果总金额大于200，youhuisum就减10元，否则就继续判断总金额是否大于100，如果sum大于100，youhuisum就减20元以此类推

<!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>
        var sum = 20
        var youhuisum 
        if(sum>200){
            youhuisum = sum - 10
        }else if(sum>100){
            youhuisum = sum - 20
        }else if(sum>50){
            youhuisum = sum - 30
        }else{
            youhuisum = sum
        }
        console.log(sum,youhuisum)
    </script>
</body>
</html>