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
# 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>