js特殊语法∶
1,语句以;结尾,如果一行只有一条语句则;可以省略(不建议)
2.变量的定义使用var关键字,也可以不使用
用:定义的变量是局部变量
不用:定义的变量是全局变量(不建议)
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Title</title> <script> var a = 3; alert(a); // b = 4; // alert(b); var b; function fun() { b = 4; } fun(); alert(b) </script> </head> <body> </body> </html>
JavaScript_语法_流程控制语句
if. . . else . . .
switch:
在Java中,switch语句可以接受的数据类型 :byte int shor char,枚举(1.5),String(1.7)
switch(变量)
case 值
在JS中,switch语句可以接受任意的原始数据类型
while
do . . . while
for
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Title</title> <script> var a = true; switch (a) { case 1: alert("number"); break; case "abc": alert("string"); break case true: alert("true"); case null: alert(null); case undefined: alert("undefined"); } </script> </head> <body> </body> </html>
<script> var sum = 0; var num = 1; while (num<=100){ sum+=num; num++; } alert(sum) </script>
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Title</title> <script> for (var i = 1;i<=100; i++){ sum+=i; } alert(sum) </script> </head> <body> </body> </html>