不是功能？ [英] Not a function?

问题描述

当我运行下面的代码时，我会被告知，这种谈话不是一种功能。
为什么？

 函数cat（name）{
 talk = function（）{
 alert（say meeow！）
} 
} 
 
 cat（felix）; 
 cat.talk（）
  

解决方案

'试图做的是创建一个对象，其中的函数是一个构造函数，但代码实际上在做的是将变量 talk 设置为一个函数。你需要：
$ b $ pre $ 函数cat（name）{
this.talk = function（）{
alert （say meeow！）
}
}

var myCat =新猫（felix）;
myCat.talk（）


编辑：

相关javascript技术讨论： http://www.youtube.com/watch?v = ljNi8nS5TtQ

他谈到了用约30分钟的时间构建函数的对象。他发布的代码是：

 函数Circle（radius）{
 this.radius = radius; 
 this.area = function（）{
 return this.radius * this.radius * Math.PI; 
}; 
} 
 var instance = {}; 
 Circle.call（instance，5）; 
 instance.area（）; // ==> 78.5398 
 var instance2 = new Circle（5）; 
 instance2.area（）// ==> 78.5398 
 instance instanceof Circle // ==> false 
 instance2 instanceof Circle // ==>真
  

以及相关的引用：

new关键字只是一个简写，即创建一个新对象
并在其上调用构造函数... new关键字没有其他
含义

换句话说，当他使用 new 关键字时，您正在定义你的变量作为一个对象，并在该对象的上下文中调用该函数（ this 指向你的对象）。

new 关键字所做的额外事情是将新创建的对象的原型设置为构造函数的原型。因此，如果我们这样做：

pre $ 函数Circle（radius）{
this.radius = radius;
this.area = function（）{
return this.radius * this.radius * Math.PI;
};
}
var instance = {};
Circle.call（instance，5）;
实例.__ proto__ = Circle.prototype; //我们将新对象的原型设置为构造函数的原型
instance.area（）; // ==> 78.5398
var instance2 = new Circle（5）;
instance2.area（）// ==> 78.5398
instance instanceof Circle // ==> true //现在是真的
instance2 instanceof Circle // ==> true


实例instanceof Circle 现在成立。

When I run the following code I get told, that talk is not a function. Why?

function cat(name) {
    talk = function() {
        alert(" say meeow!" )
    }
} 

cat("felix");
cat.talk()

解决方案

What you're trying to do is create an object for which the function is a constructor, but what the code is actually doing is setting the variable talk to a function. You want:

function cat(name) {
    this.talk = function() {
        alert(" say meeow!" )
    }
} 

var myCat = new cat("felix");
myCat.talk()

edit:

Relevant javascript tech talk: http://www.youtube.com/watch?v=ljNi8nS5TtQ

He talks about constructing objects with functions at about 30 minutes in. The code he posts is:

function Circle(radius){
    this.radius = radius;
    this.area = function(){
        return this.radius * this.radius * Math.PI;
    };
}
var instance = {};
Circle.call(instance, 5);
instance.area(); // ==> 78.5398
var instance2 = new Circle(5);
instance2.area() // ==> 78.5398
instance instanceof Circle // ==> false
instance2 instanceof Circle // ==> true

And the relevant quote:

The new keyword is just a shorthand that is saying "make a new object and call the constructor on it ... the new keyword has no other meaning"

In other words, he's saying that when using the new keyword, you're defining your variable as an object and calling the function in the context of that object (this points to your object).

The extra thing that the new keyword does is set the prototype of the newly made object to the prototype of the constructor. So if we do:

function Circle(radius){
    this.radius = radius;
    this.area = function(){
        return this.radius * this.radius * Math.PI;
    };
}
var instance = {};
Circle.call(instance, 5);
instance.__proto__ = Circle.prototype; // we set the prototype of the new object to that of the constructor
instance.area(); // ==> 78.5398
var instance2 = new Circle(5);
instance2.area() // ==> 78.5398
instance instanceof Circle // ==> true // this is now true 
instance2 instanceof Circle // ==> true

instance instanceof Circle is now true.

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