HTML之JavaScript分支结构
if switch
html
<!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>
/*
if
if(表达式){
语句1;
}eles if(){
语句2;
}else{
语句3;
}
1.非空字符串('xxx')会判断为true，空字符('')串会判断为false
2.非空对象 会判断为true，null和undefined会判断为false
3.非0的number会判断为true，0会判断为false
switch 跟Java语法一样（跟C语言也没啥逻辑区别）
switch(表达式){
case 值1:
语句1;
break;
case 值2:
语句2;
break;
case 值3:
语句3;
break;
default:
语句4;
break;
}
*/
if ("false") {
console.log('true');
} else {
console.log('false');
}
//根据月份输出季节
var month = prompt('请输入月份');//弹窗输入 返回结果为用户在窗口上输入的值，以string类型返回
console.log(typeof month);
month = Number.parseInt(month);//将字符串转换为数字
console.log(typeof month);
if (month >= 3 && month <= 5) {
console.log('春季');
} else if (month == 6 || month == 7 || month == 8) {
console.log('夏季');
} else if (month == 9 || month == 10 || month == 11) {
console.log('秋季');
} else if (month == 12 || month == 1 || month == 2) {
console.log('冬季');
} else {
console.log('输入错误');
}
switch (month) {
case 3:
case 4://条件穿透 跟Java一样
case 5:
console.log('春季');
break;
case 6:
case 7:
case 8:
console.log('夏季');
break;
case 9:
case 10:
case 11:
console.log('秋季');
break;
case 12:
case 1:
case 2:
console.log('冬季');
break;
default:
console.log('输入错误');
break;
}
</script>
</head>
<body>
</body>
</html>