blocks|key|4037828|text|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4037829|“如果add()函数已经是由'this‘调用的方法，那么核心应用()函数实现的目的或用途是什么。”|blockquote|4037830|4037831|4037832|这样arguments就可以作为整个集合传递。如果Set接受不确定数量的参数，则此函数非常有用。|offset|length|style|CODE|4037833|entityMap^0|0|0|0|0|2|9|P|3|0^^$0|@$1|2|3|-4|4|5|6|N|7|@]|8|@]|9|$]]|$1|A|3|B|4|C|6|O|7|@]|8|@]|9|$]]|$1|D|3|-4|4|5|6|P|7|@]|8|@]|9|$]]|$1|E|3|-4|4|5|6|Q|7|@]|8|@]|9|$]]|$1|F|3|G|4|5|6|R|7|@$H|S|I|T|J|K]|$H|U|I|V|J|K]]|8|@]|9|$]]|$1|L|3|-4|4|5|6|W|7|@]|8|@]|9|$]]]|M|$]]

<blockquote>
 "if the add() function is already a method called by 'this' then what purpose or use is the core apply() function fulfilling."
</blockquote>

So that the <code>arguments</code> can be passed on as an entire collection. Useful if <code>Set</code> accepts an indefinite number of arguments.

blocks|key|4037872|text|构造函数中不需要它--事实上，它与一般的构造函数没有任何关系(但显然它与这个特定的构造函数有关;-)。apply所做的就是确保目标函数被“正确”调用。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4037873|也就是说，apply，当给定一个类似数组的对象*+(arguments计数)、[n1,+n2,+...+n3]和一个函数f时，它会将目标函数调用为f(n1,+n2,+...+n3)。apply还接受"this+context“，该上下文在代码中传递给新创建的对象(以使其看起来好像add是”作为普通方法“被调用的)。有关更多信息/示例，请参阅上面的链接。|4037874|这意味着，对于上面的代码，|4037875|var+s+=+new+Set(1,+2,+3)|code-block|syntax|javascript|4037876|和|4037877|var+s+=+new+Set()
s.add(1,+2,+3)|4037878|是等价的。|4037879|祝你编码愉快。|4037880|4037881|*在FireFox+4之前的版本中，它必须是数组本身。这就是为什么有时代码会使用丑陋的习惯用法：|4037882|f.apply(context,+Array.prototype.slice.call(arguments,+0))|4037883|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/function/apply^0|1F|5|1F|5|0|0|5|5|Q|9|13|G|1O|1|21|H|2J|5|3W|3|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|19|8|@$9|1A|A|1B|B|C]]|D|@$9|1C|A|1D|1|1E]]|E|$]]|$1|F|3|G|5|6|7|1F|8|@$9|1G|A|1H|B|C]|$9|1I|A|1J|B|C]|$9|1K|A|1L|B|C]|$9|1M|A|1N|B|C]|$9|1O|A|1P|B|C]|$9|1Q|A|1R|B|C]|$9|1S|A|1T|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|1U|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|1V|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|1W|8|@]|D|@]|E|$]]|$1|Q|3|R|5|L|7|1X|8|@]|D|@]|E|$M|N]]|$1|S|3|T|5|6|7|1Y|8|@]|D|@]|E|$]]|$1|U|3|V|5|6|7|1Z|8|@]|D|@]|E|$]]|$1|W|3|-4|5|6|7|20|8|@]|D|@]|E|$]]|$1|X|3|Y|5|6|7|21|8|@]|D|@]|E|$]]|$1|Z|3|10|5|L|7|22|8|@]|D|@]|E|$M|N]]|$1|11|3|-4|5|6|7|23|8|@]|D|@]|E|$]]]|12|$13|$5|14|15|16|E|$17|18]]]]

It isn't need in the constructor -- in fact, it has nothing to do with a constructor in general (but obviously it matters for this specific one ;-). What <a href="https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/function/apply" rel="nofollow"><code>apply</code></a> does do is ensure that the target function is invoked "correctly".

That is, <code>apply</code>, when given an array-like object* (<code>arguments</code> counts), <code>[n1, n2, ... n3]</code> and a function <code>f</code>, it will call the target function as <code>f(n1, n2, ... n3)</code>. <code>apply</code> also takes the "this context" which is passed the newly created object in the code (to make it seem as though <code>add</code> was called "as a normal method"). See the link above for more information/examples.

That means, that for the code above,

<pre><code>var s = new Set(1, 2, 3)
</code></pre>

and

<pre><code>var s = new Set()
s.add(1, 2, 3)
</code></pre>

are equivalent.

Happy coding.

<hr>

*In FireFox prior to 4 it had to be an Array-proper. This is why sometimes code uses the ugly idiom:

<pre><code>f.apply(context, Array.prototype.slice.call(arguments, 0))
</code></pre>

blocks|key|2422506|text|我相信调用它不是为了作用域，而是apply将接受一个参数数组并按顺序传递它们：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2422507|this.add.apply(this,+[1,2,3,4]);
....
function+add(one,+two,+three,+four)|code-block|syntax|javascript|2422508|没有一个参数是数组|2422509|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I believe it is being called not for the scope, but the fact that apply will take an array of arguments and pass them in order:

<pre><code>this.add.apply(this, [1,2,3,4]);
....
function add(one, two, three, four)
</code></pre>

not a single parameter that is an array

blocks|key|2422570|text|函数的apply方法允许您通过传递数组而不是项列表来调用函数。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2422571|举例说明：|2422572|function+add(a,+b)+{
++++return+a%2Bb;
}

var+values+=+[1,2];

alert(add.apply(this,+values));|code-block|syntax|javascript|2422573|将发出3级警报。|2422574|2422575|因此，从本质上讲，您所做的就是允许构造函数接受任意数量的参数，然后将它们一次性传递给add函数。|2422576|因此，如果您使用以下命令调用您的构造函数：|2422577|var+stack+=+new+Set(1,2,3,4,5,6,7,8,9);|2422578|所有这些值都将被传递给add函数，就像您已经编写了：|2422579|this.add(1,2,3,4,5,6,7,8,9);|2422580|entityMap^0|3|5|0|0|0|0|0|16|3|0|0|0|B|3|0|0^^$0|@$1|2|3|4|5|6|7|11|8|@$9|12|A|13|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|14|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|15|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|16|8|@]|D|@]|E|$]]|$1|O|3|-4|5|6|7|17|8|@]|D|@]|E|$]]|$1|P|3|Q|5|6|7|18|8|@$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|R|3|S|5|6|7|1B|8|@]|D|@]|E|$]]|$1|T|3|U|5|J|7|1C|8|@]|D|@]|E|$K|L]]|$1|V|3|W|5|6|7|1D|8|@$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|X|3|Y|5|J|7|1G|8|@]|D|@]|E|$K|L]]|$1|Z|3|-4|5|6|7|1H|8|@]|D|@]|E|$]]]|10|$]]

The <code>apply</code> method of a function allows you to invoke the function by passing an array instead of a list of items.

To illustrate:

<pre><code>function add(a, b) {
 return a+b;
}

var values = [1,2];

alert(add.apply(this, values));
</code></pre>

will alert 3.

<hr>

So, essentially, what you are doing there is allowing your constructor to take any number of arguments, and you will then pass them all in to the <code>add</code> function in one shot.

So, if you were to call your constructor with:

<pre><code>var stack = new Set(1,2,3,4,5,6,7,8,9);
</code></pre>

all of those values will be passed to the <code>add</code> function, as if you would have written:

<pre><code>this.add(1,2,3,4,5,6,7,8,9);
</code></pre>

blocks|key|2422624|text|使用.apply()语法允许您将参数数组传递给被调用的函数。在本例中，它传递的是arguments对象，这意味着它使用传递给Set构造函数的任何和所有参数调用add()。因此，您可以创建具有任意数量的值的新Set对象，例如，|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2422625|var+mySet+=+new+Set(13,42,18,19,44,11,5);|code-block|syntax|javascript|2422626|所有这些值都将传递给add()。|2422627|entityMap^0|2|8|14|9|27|5|0|0|A|5|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|N|$]]

Using the <code>.apply()</code> syntax allows you to pass an array of arguments to the function being invoked. In this case it is passing the <code>arguments</code> object, which means it is calling <code>add()</code> with any and all of the parameters that were passed to the Set constructor function. So you can create new Set objects with an arbitrary number of values by saying, e.g.,

<pre><code>var mySet = new Set(13,42,18,19,44,11,5);
</code></pre>

And all of those values will be passed through to <code>add()</code>.

<pre><code>function Set() { // This is the constructor
 this.values = {}; 
 this.n = 0; 
 this.add.apply(this, arguments); // All arguments are values to add
}

// Add each of the arguments to the set.
Set.prototype.add = function() {
 /* Code to add properties to the object's values property */
 return this;
};
</code></pre>

This is the beginning of the code used in "Javascript: The Definitive Guide" to create a 'Set' Class. I've tried to rationalize the necessity of the <a href="https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Function/apply" rel="nofollow"><code>apply()</code></a> function in the constructor but can not figure it out for the life of me.

<pre><code>this.add.apply(this, arguments);
</code></pre>

if the <code>add()</code> function is already a method called by '<code>this</code>' then what purpose or use is the core <a href="https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Function/apply" rel="nofollow"><code>apply()</code></a> function fulfilling. Thanks in advance to anyone who attempts to explain this to me

<a href="http://jsfiddle.net/Marlin/Ydwgv/" rel="nofollow">http://jsfiddle.net/Marlin/Ydwgv/</a> - Full Example from Javascript: The Definitive Guide

Why is the apply() function needed in the constructor

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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function Set() {          // This is the constructor    this.values = {};         this.n = 0;              this.add.apply(this, arguments);  // All arguments ar...

问为什么构造函数中需要应用()函数
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