Javascript Alert框未显示
[英]Javascript Alert box is not showing
问题描述
I am currently learning Object oriented Javascript but it seems that the alert is not working. 
我目前正在学习面向对象的Javascript，但似乎警报不起作用。 what is the problem here? 这里有什么问题？
<
html>
<head>
<script>
function professor(name, myLecture){
this.name = name;
this.myLecture = myLecture;
}
professor.prototype.display = function(){
return this.name + " is teaching " + this.myLecture;
};
function subjectList(subject){
this.subject = subject;
}
subjectList.prototype.showAll= function(){
var str = " " ;
for(var i = 0 ; i<subject.length; i++ )
str+= this.subject[i].display();
return str;
};
var ListOfSubs = new subjectList([
new professor("Muy","Obprog")
]);
alert(ListOfSubs.showAll());
</script>
<body>
</body>
</head>
</html>
5 个解决方案
解决方案1
2 已采纳 2012-03-20 13:42:43
应该this.subject.length代替subject.length 。
解决方案2
1 2012-03-20 13:55:22
The line: 该行：
for(var i = 0 ; i<subject.length; i++ )
The error was that "Subject is not defined". 错误是“未定义主题”。 Changing it from subject.length = this .subject.length should fix your problem. 更改为subject.length = this .subject.length应该可以解决您的问题。
It should output: 它应该输出：
Muy is teaching Obprog
解决方案3
0 2012-03-20 13:42:34
You need this. 你需要this.
subjectList.prototype.showAll= function(){
var str = " " ;
for(var i = 0 ; i< this.subject.length; i++ ) // notice this.subject
str+= this.subject[i].display();
return str;
};
解决方案4
0 2012-03-20 14:21:12
Other have informed you about the reason what is wrong with your js-code. 其他人已通知您有关js代码出问题的原因。
One more note from me. 还有我的一张纸条。
Usually an programmed alert will not come up when an exception happens before. 通常，在之前发生异常时，不会发出编程的警报。
And by the way, your body-tag should be after the closing head-tag 顺便说一句，您的身体标签应该在关闭的头部标签之后
解决方案5
0 2012-03-20 14:30:57
This code will work inside your script tag: 此代码将在您的脚本标签内运行：
function professor(name, myLecture){
this.name = name;
this.myLecture = myLecture;
}
professor.prototype.display = function(){
return this.name + " is teaching " + this.myLecture;
};
function subjectList(subject){
this.subject = subject;
}
subjectList.prototype.showAll= function(){
var str = " " ;
for(var i = 0 ; i<subject.length; i++ )
str+= this.subject[i].display();
return str;
};
var ListOfSubs = new subjectList([
new professor("Muy","Obprog")
]);
alert(ListOfSubs.showAll());
Cause: in your showAll function you have used subject, which is not existent, but the object of your prototype has a member called subject. 原因：在showAll函数中，您使用的主题不存在，但原型的对象具有一个称为主题的成员。 So instead of i<subject.length , i<this.subject.length is fixing your problem. 因此，而不是i<subject.length ， i<this.subject.length是修复你的问题。
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