blocks|key|2310261|text|var表达式正在被函数表达式Command.prototype.run关闭。这称为闭包。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2310262|var+Command+=+function+()+{
++++var+text+=+'Hello+World';

++++Command.prototype.run+=+function+()+{++//+text+is+closed+over+by+this+function
++++++++console.log(text);
++++};
};
Command.prototype.run1+=+function+()+{+//+text+is+not+in+scope+and+thus+not+available.
++++console.log(text);
};

var+command+=+new+Command();
command.run();++//+this+will+work+and+display+what+is+in+text
command.run1();++//+this+will+fail+and+throw+text+undefined+error.|code-block|syntax|javascript|2310263|通常，如果变量在定义函数的作用域中，则该变量将可用于该函数。如果不是，那么您将无法访问它。|2310264|entityMap^0|E|L|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

The var <code>test</code> is being closed over by the function expression <code>Command.prototype.run</code>. This is called closure.

<pre><code>var Command = function () {
 var text = 'Hello World';

 Command.prototype.run = function () { // text is closed over by this function
 console.log(text);
 };
};
Command.prototype.run1 = function () { // text is not in scope and thus not available.
 console.log(text);
};

var command = new Command();
command.run(); // this will work and display what is in text
command.run1(); // this will fail and throw text undefined error.
</code></pre>

Generally if a variable is in scope where you define the function it will be available to that function. If not then you don't have access to it.

blocks|key|2310271|text|Prototype使用具有内存管理优势。如果你不使用prototype，当你创建新对象时，你将不得不用这个来创建新函数。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2310272|var+Command+=+function+()+{
++++var+text+=+'Hello+World';

++++//One+time+create+this+function
++++Command.prototype.run+=+function+()+{
++++++++console.log(text);
++++};

+++++this.test=+function(){
+++++++console.log(text);
+++++}
};

var+command+=+new+Command();+//again+created+test+function,+because+it+doesn't+have+a+prototype
command.run();
command.test();|code-block|syntax|javascript|2310273|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Prototype using has memory management advantages.
If you don't use prototype, when you create new object, you will have to create new function with this.

<pre><code>var Command = function () {
 var text = 'Hello World';

 //One time create this function
 Command.prototype.run = function () {
 console.log(text);
 };

 this.test= function(){
 console.log(text);
 }
};

var command = new Command(); //again created test function, because it doesn't have a prototype
command.run();
command.test();
</code></pre>

blocks|key|410995|text|如果在函数内部的函数原型上设置run()函数，则每次运行函数时都会重新定义该函数。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|410996|这是没有意义的(因为你可以只定义另一个函数，而不是设置原型)，效率低下(因为你一遍又一遍地做相同的工作)，另一个看着你的代码的开发人员不会理解你为什么要这样做，而你可以在函数之外定义它。|410997|这就是为什么你看不到其他人这样做的原因。在原型上的函数外部定义run()只需定义一次。这是惯用的JS，例如。MDN。|410998|我没有意识到这样做有任何技术上的问题。|410999|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/prototype^0|F|5|0|0|V|5|1I|3|0|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|W|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|X|8|@$9|Y|A|Z|B|C]]|D|@$9|10|A|11|1|12]]|E|$]]|$1|J|3|K|5|6|7|13|8|@]|D|@]|E|$]]|$1|L|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|M|$N|$5|O|P|Q|E|$R|S]]]]

If you set the <code>run()</code> function on a function's prototype inside the function, then it will be redefined every time the function is run.

That's pointless (as you could just define another function rather than setting the prototype), inefficient (as you're doing identical work over and over again) and another developer looking at your code won't understand why you did it when you could have defined it outside the function.

That'll be why you don't see other people doing it. Defining <code>run()</code> outside your function on the prototype defines it once. It's idiomatic JS, eg. <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/prototype" rel="nofollow">MDN</a>.

I'm not aware of any technical problem with doing it.

i have a question about JavaScript. I know how to use prototype, and why is it used, but i have tried to answer me this question, what will happen if i use prototype in a function like this,

<pre><code>var Command = function () {
 var text = 'Hello World';

 Command.prototype.run = function () {
 console.log(text);
 };
};

var command = new Command();
command.run();
</code></pre>

Now I will be able to use also the private functions or variables. I have build with jsFiddle examples, with all variants and it shows that there seems no difference where I used prototype. But may I have overlocked something?

Javascript / Prototype

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有一个关于JavaScript的问题。我知道如何使用prototype，以及为什么使用它，但我试图回答这个问题，如果我在这样的函数中使用prototype会发生什么，var Command = function () {    var text = 'Hello World';    Command.prototyp...

问Javascript / Prototype
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