blocks|key|1055536|text|如果Object.keys(arguments).length是一个对象，那么arguments也可以工作：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1055537|​|1055538|let+arguments+=+['foo',+'bar',+'baz'];

console.log('Array',+Object.keys(arguments).length);

arguments+=+{+1:+'foo',+2:+'bar',+3:+'baz'+}

console.log('Object',+Object.keys(arguments).length);|code-block|syntax|javascript|1055539|1055540|也就是说，如果输入值已知为数组(+arguments是)，那么使用Object.keys是绝对没有必要的。|1055541|entityMap^0|2|T|13|9|0|0|0|0|H|9|X|B|0^^$0|@$1|2|3|4|5|6|7|R|8|@$9|S|A|T|B|C]|$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|W|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|X|8|@]|D|@]|E|$K|L]]|$1|M|3|G|5|6|7|Y|8|@]|D|@]|E|$]]|$1|N|3|O|5|6|7|Z|8|@$9|10|A|11|B|C]|$9|12|A|13|B|C]]|D|@]|E|$]]|$1|P|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|Q|$]]

<p><code>Object.keys(arguments).length</code> Would also work if <code>arguments</code> is an object:</p>
<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>let arguments = ['foo', 'bar', 'baz'];

console.log('Array', Object.keys(arguments).length);

arguments = { 1: 'foo', 2: 'bar', 3: 'baz' }

console.log('Object', Object.keys(arguments).length);</code></pre>
</div>
</div>
</p>
<p>That said, if the input value is known to be an array (which <code>arguments</code> is), it's absolutely unecessary to use <code>Object.keys</code>.</p>


blocks|key|2047686|text|arguments是一个“异域对象”，它是“类似数组的”--它具有数值属性和.length。与Object.keys一起使用它与Object.keys(someArray)一样有意义，也就是说，没有。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2047687|在新代码中，最好完全避免使用arguments，因为它具有一些不透明的特性，比如参数变量的不可见突变。示例：|2047688|​|2047689|function+someFunctionThatMutatesArray(a)+{
++++a[0]+=+'hey'
}

function+func(xyz)+{
++++someFunctionThatMutatesArray(arguments)
++++console.log(xyz)+//+surprise
}

func(100)|code-block|syntax|javascript|2047690|2047691|entityMap^0|0|9|12|7|1B|B|1S|M|0|E|9|0|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@$9|S|A|T|B|C]|$9|U|A|V|B|C]|$9|W|A|X|B|C]|$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|13|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|14|8|@]|D|@]|E|$M|N]]|$1|O|3|I|5|6|7|15|8|@]|D|@]|E|$]]|$1|P|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|Q|$]]

<p><code>arguments</code> is an &quot;exotic object&quot; which is &quot;array-like&quot; - it has numeric properties and <code>.length</code>. Using <code>Object.keys</code> with it makes as much sense as <code>Object.keys(someArray)</code>, that is, none.</p>
<p>In new code it's better to avoid <code>arguments</code> altogether because of its shady features, like invisible mutation of argument variables. Example:</p>
<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>function someFunctionThatMutatesArray(a) {
    a[0] = 'hey'
}

function func(xyz) {
    someFunctionThatMutatesArray(arguments)
    console.log(xyz) // surprise
}

func(100)</code></pre>
</div>
</div>
</p>


blocks|key|1485837|text|没有理由使用Object.keys(arguments).length来获取传递给函数的参数的计数。该值总是与arguments.length相同，因此充其量是多余的。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1485838|由于您有性能标记，我要补充的是，Object.keys().length可能会慢一些。然而，它也不太可能产生很大的整体影响。|1485839|​|1485840|function+test()+{
++const+keysLength+=+Object.keys(arguments).length;
++const+argsLength+=+arguments.length;
++console.log(+`keys:+[${keysLength}]+arguments:+[${argsLength}]+equal:+[${keysLength+===+argsLength}]`+);
}

test();
test(1);
test(1,+2);
test(1,+2,+null);
test(1,+2,+undefined,+4);
test(1,+2,+undefined,+4,+["a",+"b",+"c"]);
test({foo:+"hello",+bar:+"world"});
test({foo:+"hello",+bar:+"world"});|code-block|syntax|javascript|1485841|.as-console-wrapper+{+max-height:+100%25+!important;+}|1485842|1485843|entityMap|0|LINK|mutability|MUTABLE|url|/questions/tagged/performance^0|6|T|1J|G|0|G|K|4|2|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Z|8|@$9|10|A|11|B|C]|$9|12|A|13|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|14|8|@$9|15|A|16|B|C]]|D|@$9|17|A|18|1|19]]|E|$]]|$1|H|3|I|5|6|7|1A|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|1B|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|L|7|1C|8|@]|D|@]|E|$M|N]]|$1|Q|3|I|5|6|7|1D|8|@]|D|@]|E|$]]|$1|R|3|-4|5|6|7|1E|8|@]|D|@]|E|$]]]|S|$T|$5|U|V|W|E|$X|Y]]]]

<p>There is no reason to use <code>Object.keys(arguments).length</code> to get the count of the passed in arguments for a function. The value is always going to be identical to <code>arguments.length</code>, so it is superfluous at best.</p>
<p>Since you have <a href="/questions/tagged/performance" class="post-tag" title="show questions tagged &#39;performance&#39;" rel="tag">performance</a> tag, I would add that <code>Object.keys().length</code> is likely to be slower. <em>However</em>, it is also unlikely to have much of an impact overall.</p>
<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>function test() {
  const keysLength = Object.keys(arguments).length;
  const argsLength = arguments.length;
  console.log( `keys: [${keysLength}] arguments: [${argsLength}] equal: [${keysLength === argsLength}]` );
}

test();
test(1);
test(1, 2);
test(1, 2, null);
test(1, 2, undefined, 4);
test(1, 2, undefined, 4, ["a", "b", "c"]);
test({foo: "hello", bar: "world"});
test({foo: "hello", bar: "world"});</code></pre>
<pre class="snippet-code-css lang-css prettyprint-override"><code>.as-console-wrapper { max-height: 100% !important; }</code></pre>
</div>
</div>
</p>


<p>I'm new to JS and trying to understand something I read in a couple of places:</p>
<p>While trying to get the number of arguments received to a function, there was use of
<code>Object.keys(arguments).length</code>. However, as far as I could find, there isn't any benefit for this and the shorter way would be to just use <code>arguments.length</code></p>
<p>This is because <code>arguments</code> holds the <code>.length</code> property.
(<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/arguments" rel="nofollow noreferrer">MDN doc - The arguments object</a>)</p>
<p>Is there somethings I'm missing?
Are there situations where using <code>object.keys()</code> is preferred on terms of performance or safety?</p>
<p>Thank you.</p>


Using object.keys(arguments).length VS arguments.length

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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我对JS很陌生，我试着理解我在几个地方读到的东西：在尝试获取函数收到的参数数时，使用了Object.keys(arguments).length。然而，据我所知，这没有任何好处，更短的方法是只使用arguments.length这是因为arguments拥有.length属性。()有什么东西我遗漏了吗？在某些情况下，在...

问使用object.keys(参数).length VS arguments.length
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问使用object.keys(参数).length VS arguments.lengthEN