JavaScript声明
<script></script>
基本输出
<script> document.write("<h1>Hello World!</h1>"); </script>
外部引用
<script src="demo.js"></script>
变量声明
var x=125; var msg="Hello World"; console.log(x); console.log(msg);
变量命名规则
有效字符，只能由字母、数字和下划线组成，且以字母或下划线开头。
数据类型
- undefined未定义
- null空
- boolean布尔
- number数字
- string字符串
<script> var x; document.write(typeof(x) + "<br/>"); var y = ''; document.write(typeof(y) + "<br/>"); var b = true; document.write(typeof(b) + "<br/>"); var n = 520; document.write(typeof(n) + "<br/>"); var s = "幸福安康"; document.write(typeof(s) + "<br/>"); </script>
if分支结构
<script> var sex = 11; if (sex == 11) { document.write("男性"); } else { document.write("女性"); } </script>
if多分支结构
<script> var month = 12; if (month == 12 || month == 1 || month == 2) { document.write("冬季"); } else if (month == 3 || month == 4 || month == 5) { document.write("春季"); } else if (month == 6 || month == 7 || month == 8) { document.write("夏季"); } else if (month == 9 || month == 10 || month == 11) { document.write("秋季"); } else { document.write("不是地球公转周期"); } </script>
switch 语句
<script> var key=1; switch (key) { case 1:document.write("星期一");break; case 2:document.write("星期二");break; case 3:document.write("星期三");break; case 4:document.write("星期四");break; case 5:document.write("星期五");break; case 6:document.write("星期六");break; case 7:document.write("星期七");break; default:document.write("星期八?");break; } </script>
while循环语句
<script> var i=1; var sum=0; while (i<=100) { sum+=i; i++; } document.write("1++100的结果是："+sum); </script>
do-while循环语句
<script> var i = 1; var sum = 0; do { sum += i; i++; } while (i <= 100); document.write("1++100的结果是：" + sum); </script>
for循环语句
<script> var sum = 0; for (var i = 0; i < 101; i++) { sum+=i; } document.write("for循环1++100的结果是：" + sum); </script>
break和continue语句
<script> for (var i = 0; i < 10; i++) { if (i % 2 == 0) { document.write(i); continue; } if (i == 7) { document.write(i + "停止"); break; } document.write("数字" + i); } </script>
嵌套for循环
<script> for (var i = 1; i < 10; i++) { for (var j = 1; j <= i; j++) { document.write(j + "*" + i + "=" + (j * i) + " "); } document.write("<br/>"); } </script>
