为什么此继承示例在我的计算机上不起作用？
[英]Why does this example of inheritance not work on my computer?
问题描述
I have some Java background but now I am trying to write some simple games in JavaScript and HTML. 
我有一些Java背景，但是现在我正尝试用JavaScript和HTML编写一些简单的游戏。 I'm struggling to understand how OOP works because it seems like there are different ways of creating objects? 我正在努力了解OOP的工作原理，因为似乎存在创建对象的不同方法？ I wrote this snippet referencing a friend's code but the console gives me "uncaught TypeError: Cannot set property 'roar' of undefined". 我写了引用朋友代码的代码段，但是控制台给了我“未捕获的TypeError：无法设置未定义的属性'roar'”。 Why does the code work for him but not for me? 为什么该代码对他有效，但对我无效？ Is he running some kind of server side library? 他在运行某种服务器端库吗？
test.js: test.js：
function Animal() {
this.needsAir = true;
this.roar = function() {
console.log("roar");
}
}
function Bear() {
Animal.call();
}
var init = function() {
var bear = new Bear();
bear.roar();
console.log(bear.needsAir)
}
index.html: index.html：
<html>
<head>
<script type="text/javascript" src="./test.js"></script>
</head>
<body>
<script type="text/javascript">
window.onload = function() {
init();
}
</script>
</body>
</html>
3 个解决方案
解决方案1
6 已采纳 2015-09-04 00:23:19
You need to pass this to .call . 您需要this传递给.call 。
function Bear() {
Animal.call(this);
}
Also, your prototype inheritance isn't complete as well. 另外，您的原型继承也不完整。
解决方案2
0 2015-09-04 00:29:53
Your functions have different this -- try to use the apply methods, which would get you somewhat further, like; 您的函数与this有所不同-尝试使用apply方法，这会使您更进一步，例如；
function Bear() {
Animal.apply(this);
}
There are a lot more in javascript which is needed, such as prototype definitions 在javascript中还有很多需要的东西，例如原型定义
解决方案3
0 2015-09-04 00:30:55
your Bear function needs to pass this to Animal call. 您的Bear函数需要this传递给Animal调用。
To understand javascript inheritance better you can check out this blog on understanding javascript inheritance 为了更好地了解javascript继承，您可以查看有关了解javascript继承的博客
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