一.void运算符
这个运算符用在既保留了超链接,点击超链接时执行一段js代码,但页面不能跳转。
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<p>Hello World</p>
<br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/>
<br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/>
<a href = "javascript:void(0)" onclick = "alert('111')">你好,世界</a>
</body>
</html>
注意,如果写成href = ""
,表示的是路径是一个空的字符串,而写成href = "void(0)"
,表示的路径是一个叫做void(0)的路径,只有表示成href = "javascript:void(0)"
,才说明路径为空,自然不会跳转(javascript说明后面是一段js代码)。
二.控制语句
有七个在Java学习当中介绍过,if, switch, while, do...while, for, break, continue
我们介绍两个新的
for in
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<script type = "text/javascript">
var arr = [11, "abc", false, true, 55];
for(var i = 0;i < arr.length; i++){
alert(arr[i]);
}
for(var j in arr){
alert(arr[j]);
}
</script>
</body>
</html>
作用一:遍历数组,上例子中的j代表了in后面的数组arr的下标。
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<script type = "text/javascript">
User = function(username, password){
this.username = username;
this.password = password;
}
var u = new User("张三", "1111");
alert("1" + u.username + u.password);
alert("2" + u["username"] + u["password"]);
for(var shuXingMing in u){
//alert(shuXingMing);//可以获得属性名username和password
//alert(typeof shuXingMing);//String类型
alert("3" + u[shuXingMing]);
}
</script>
</body>
</html>
作用二:遍历对象属性,上面例子中shuXingMing为变量名,是String类型的,所以本身有""号,不能写成u["shuXingMing"]
.
with
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<script type = "text/javascript">
User = function(username, password){
this.username = username;
this.password = password;
}
var u = new User("张三", "1111");
with(u){
alert(username + password);
}
</script>
</body>
</html>
用法如上例子。