if conditional judgment statement in JavaScript

if conditional judgment statement:

#If the condition is true, what code will be executed; if the condition is not true, what code will be executed

Structure 1: Only judge true (true), if the condition is false, do nothing

if (Conditional judgment: the judgment result is a Boolean value)

{

The condition is true (true), the executed code

}

## Structure 2: Both true and false

if (Conditional judgment)

{

If the condition is true, the code to be executed

}else

{

The condition is false, the code to be executed Code

}

# Structure 3: Multi-condition judgment
if(Condition 1)

{

Code 1;

}else if(Condition 2)

{

Code 2;

}else if(condition 3)

{

Code 3;

}else

{

If none of the above conditions are true, execute this code;

}

Note: Although there are multiple conditions, there is an "OR" relationship between the conditions. . At any moment, only one condition can be true, and multiple conditions cannot be met at the same time.

<!DOCTYPE HTML>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
        <title>php.cn</title>
        <script>
        //给一个成绩
        var score=89;
        //判断成绩所属级别
        if(score<60){
            document.write("对不起，没有及格");
        }else if (score>=60&&score<70){
            document.write("刚好及格");
        }else if(score>=70&&score<80){
            document.write("成绩良好");
        }else if(score>=80&&score<90){
            document.write("成绩优秀");
        }else if(score>=90&&score<100){
            document.write("试卷这么难，这样的成绩简直逆天");
        }else{
            document.write("对不起，你的成绩超出系统判断范围，请重新输入");
        }
        
        </script>
    </head>
    <body>
    </body>
</html>

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<!DOCTYPE HTML>
<html>
 <head>
 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
 <title>php.cn</title>
 <script>
 //给一个成绩
 var score=89;
 //判断成绩所属级别
 if(score<60){
 document.write("对不起，没有及格");
 }else if (score>=60&&score<70){
 document.write("刚好及格");
 }else if(score>=70&&score<80){
 document.write("成绩良好");
 }else if(score>=80&&score<90){
 document.write("成绩优秀");
 }else if(score>=90&&score<100){
 document.write("试卷这么难，这样的成绩简直逆天");
 }else{
 document.write("对不起，你的成绩超出系统判断范围，请重新输入");
 }
 
 </script>
 </head>
 <body>
 </body>
</html>
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