blocks|key|35134|text|这不是ECMAScript+(JavaScript)的一部分。它只是一个由你的某个库定义的函数。通常是jQuery或PrototypeJS。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|35135|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

That's not part of ECMAScript (JavaScript). It's just a function defined by some library of yours. Usually jQuery or PrototypeJS.

blocks|key|2442584|text|我认为您正在处理的是一个框架。大多数框架都包含从选择器或dom对象生成自定义对象的$函数。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2442585|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

I think you're dealing with a framework here.
Most frameworks include $ functions to generate custom objects from a selector or dom object.

blocks|key|2442615|text|JavaScript语言中不包含$()方法。它通常在jQuery和Prototype等JavaScript框架中定义为DOM选择器。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2442616|有趣的是，直到2009年12月，ECMAScript规范都在声明：|2442617|2442618|标识符中的任意位置都允许使用美元符号($)和下划线(_)。美元符号仅用于机械生成的代码。+(Source)|blockquote|BOLD|2442619|2442620|2442621|然而，这个“机械生成代码的美元符号”提示被从current+ECMAScript+specification+(ECMA262-第5版/2009年12月)中删除了。|2442622|2442623|尽管如此，最初的问题可能指的是jQuery、Prototype等公司中流行的DOM选择器。下面是几个jQuery示例：|2442624|$('*');+++++++++/*+This+selector+is+a+wild+card+method+and+will+select+all+
+++++++++++++++++++elements+in+a+document.+*/

$('#id');+++++++/*+This+selector+selects+an+element+with+the+given+ID.+*/

$('.class');++++/*+The+class+selector+will+gather+all+elements+in+the+
+++++++++++++++++++document+with+the+given+class+name.+*/

$('element');+++/*+This+selector+will+collect+all+elements+in+a+document+with+
+++++++++++++++++++the+given+tag+name+i.e.+table,+ul,+li,+a+etc.+*/|code-block|syntax|javascript|2442625|您可能想要查看以下文章以获取更多示例：|2442626|2442627|jQuery+selectors+and+examples|unordered-list-item|2442628|2442629|entityMap|0|LINK|mutability|MUTABLE|url|http://jquery.com/|1|http://www.prototypejs.org/|2|http://en.wikipedia.org/wiki/Document_Object_Model|3|http://en.wikipedia.org/wiki/ECMAScript|4|https://stackoverflow.com/questions/205853/why-would-a-javascript-variable-start-with-a-dollar-sign/205974#205974|5|http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-262.pdf|6|https://www.w3schools.com/jquery/jquery_selectors.asp^0|G|3|Q|6|0|X|9|1|1N|3|2|0|G|A|3|0|0|T|F|1A|6|4|0|0|0|M|W|5|0|0|0|0|0|0|0|T|6|0|0^^$0|@$1|2|3|4|5|6|7|1P|8|@$9|1Q|A|1R|B|C]]|D|@$9|1S|A|1T|1|1U]|$9|1V|A|1W|1|1X]|$9|1Y|A|1Z|1|20]]|E|$]]|$1|F|3|G|5|6|7|21|8|@]|D|@$9|22|A|23|1|24]]|E|$]]|$1|H|3|-4|5|6|7|25|8|@]|D|@]|E|$]]|$1|I|3|J|5|K|7|26|8|@$9|27|A|28|B|L]]|D|@$9|29|A|2A|1|2B]]|E|$]]|$1|M|3|-4|5|6|7|2C|8|@]|D|@]|E|$]]|$1|N|3|-4|5|6|7|2D|8|@]|D|@]|E|$]]|$1|O|3|P|5|6|7|2E|8|@]|D|@$9|2F|A|2G|1|2H]]|E|$]]|$1|Q|3|-4|5|6|7|2I|8|@]|D|@]|E|$]]|$1|R|3|S|5|6|7|2J|8|@]|D|@]|E|$]]|$1|T|3|U|5|V|7|2K|8|@]|D|@]|E|$W|X]]|$1|Y|3|Z|5|6|7|2L|8|@]|D|@]|E|$]]|$1|10|3|-4|5|6|7|2M|8|@]|D|@]|E|$]]|$1|11|3|12|5|13|7|2N|8|@]|D|@$9|2O|A|2P|1|2Q]]|E|$]]|$1|14|3|-4|5|6|7|2R|8|@]|D|@]|E|$]]|$1|15|3|-4|5|6|7|2S|8|@]|D|@]|E|$]]]|16|$17|$5|18|19|1A|E|$1B|1C]]|1D|$5|18|19|1A|E|$1B|1E]]|1F|$5|18|19|1A|E|$1B|1G]]|1H|$5|18|19|1A|E|$1B|1I]]|1J|$5|18|19|1A|E|$1B|1K]]|1L|$5|18|19|1A|E|$1B|1M]]|1N|$5|18|19|1A|E|$1B|1O]]]]

The <code>$()</code> method is not part of the JavaScript language. It is often defined in JavaScript frameworks such as <a href="http://jquery.com" rel="nofollow noreferrer">jQuery</a> and <a href="http://www.prototypejs.org/" rel="nofollow noreferrer">Prototype</a>, as a <a href="http://en.wikipedia.org/wiki/Document_Object_Model" rel="nofollow noreferrer">DOM</a> selector.
It is interesting to note that up to until December 2009, the <a href="http://en.wikipedia.org/wiki/ECMAScript" rel="nofollow noreferrer">ECMAScript</a> specification used to state:
<blockquote>
The dollar sign ($) and the underscore
(_) are permitted anywhere in an
identifier. The dollar sign is
intended for use only in mechanically
generated code. (<a href="https://stackoverflow.com/questions/205853/why-would-a-javascript-variable-start-with-a-dollar-sign/205974#205974">Source</a>)
</blockquote>
However this &quot;dollar sign for mechanically generated code&quot; hint was removed from the <a href="http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-262.pdf" rel="nofollow noreferrer">current ECMAScript specification</a> (ECMA 262 - 5th Edition / December 2009).
<hr />
Nevertheless, the original question was probably referring to the popular DOM selectors in jQuery, Prototype, et al. Here are a few jQuery examples:
<pre><code>$('*'); /* This selector is a wild card method and will select all 
 elements in a document. */

$('#id'); /* This selector selects an element with the given ID. */

$('.class'); /* The class selector will gather all elements in the 
 document with the given class name. */

$('element'); /* This selector will collect all elements in a document with 
 the given tag name i.e. table, ul, li, a etc. */
</code></pre>
You may want to check the following article for more examples:
<ul>
<li><a href="https://www.w3schools.com/jquery/jquery_selectors.asp" rel="nofollow noreferrer">jQuery selectors and examples</a></li>
</ul>

blocks|key|35177|text|它不是JS内置的函数，而是它的原型|type|unstyled|depth|inlineStyleRanges|entityRanges|data|35178|http://www.prototypejs.org/api/utility/dollar-dollar|offset|length|35179|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|1G|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@$D|O|E|P|1|Q]]|A|$]]|$1|F|3|-4|5|6|7|R|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|C]]]]

Its not JS built in function, its Prototype 
<a href="http://www.prototypejs.org/api/utility/dollar-dollar" rel="nofollow noreferrer">http://www.prototypejs.org/api/utility/dollar-dollar</a>

blocks|key|1033320|text|$+sign不是javascript的一部分，它是javascript框架的一部分，可能是jQuery|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1033321|更多详细信息，请参阅this文章|offset|length|1033322|entityMap|0|LINK|mutability|MUTABLE|url|http://www.authenticsociety.com/blog/JavaScript_DollarSign^0|0|A|4|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

$ sign is not part of javascript it is a part of a javascript framework probably jQuery 

More details have a look at <a href="http://www.authenticsociety.com/blog/JavaScript_DollarSign" rel="nofollow noreferrer">this</a> article

blocks|key|2442764|text|对于您的问题，此函数将返回具有指定ID的DOM对象。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2442765|例如，如果您的HTML上有：|2442766|<div+id="thisIsMyDivId">This+is+some+content</div>|code-block|syntax|javascript|2442767|您可以使用以下命令获取DIV元素：|2442768|var+myDiv+=+$('thisIsMyDivId');|2442769|此函数的思想是取代使用document.getElementById来完成此操作的必要性。|2442770|这里的每个人都已经did...It的不是原生JS函数，它是在一些框架(Prototype和jQuery+AFAIK)上实现的。|2442771|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

Answering to your question, this function return the DOM object with the specified ID.

For example, if you have on your HTML:

<pre><code>
&lt;div id="thisIsMyDivId"&gt;This is some content&lt;/div&gt;
</code></pre>

You can get the DIV element using:

<pre><code>
var myDiv = $('thisIsMyDivId');
</code></pre>

The idea of this function is to replace the necessity of use document.getElementById to do this.

And......repeating what everyone here already did...It is not a native JS function, it is implemented on some Frameworks (Prototype and jQuery AFAIK).

blocks|key|783054|text|所提供的答案根本不是真的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|783055|​|783056|📷|atomic|offset|length|783057|783058|在这张照片中(在Chrome+about:blank标签上拍摄)，你可以清楚地看到没有jQuery。考虑到文档是空白的，所以也没有PrototypeJS。与所有其他答案相反，这是一个可以在任何网站上使用的原生JavaScript函数。|style|CODE|783059|下图显示了函数定义。|783060|783061|783062|783063|ƒ+$(selector,+[startNode])+{+[Command+Line+API]+}|code-block|syntax|javascript|783064|如果这还不够令人信服，下面是来自jQuery的函数定义：|783065|ƒ+(a,b)+{return+new+n.fn.init(a,b)}|783066|下面是PrototypeJS中的函数。|783067|function+$(element)+{
++++if+(arguments.length+>+1)+{
++++++for+(var+i+=+0,+elements+=+[],+length+=+arguments.length;+i+<+length;+i%2B%2B)
++++++++elements.push($(arguments[i]));
++++++return+elements;
++++}

++++if+(Object.isString(element))
++++++element+=+document.getElementById(element);
++++return+Element.extend(element);
++}|783068|我不同意这段代码经过适当优化的说法，我肯定会这样写|783069|function+$(element)+{
++++if+(arguments.length+>+1)+{
++++++++let+elements+=+[];
++++++++for+(let+i+in+arguments)+elements.push($(arguments[i]));
++++++++return+elements;
++++++++//or+simply+`return+arguments;`+without+the+loop+and+extra+variable
++++}
++++return+Object.isString(element)+&&+(e+=+document.getElementById(element)),+Element.extend(element)
}|783070|entityMap|0|IMAGE|mutability|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/yehe-900000/ef82e1352b3337f1620b4864304c2d1f.png|imageAlt|1|https://ask.qcloudimg.com/http-save/yehe-900000/603d33487538cb7812504a8c8facb120.png^0|0|0|0|1|0|0|0|F|B|0|0|0|0|1|1|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|1M|8|@]|9|@$G|1N|H|1O|1|1P]]|A|$]]|$1|I|3|C|5|6|7|1Q|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|1R|8|@$G|1S|H|1T|L|M]]|9|@]|A|$]]|$1|N|3|O|5|6|7|1U|8|@]|9|@]|A|$]]|$1|P|3|C|5|6|7|1V|8|@]|9|@]|A|$]]|$1|Q|3|E|5|F|7|1W|8|@]|9|@$G|1X|H|1Y|1|1Z]]|A|$]]|$1|R|3|C|5|6|7|20|8|@]|9|@]|A|$]]|$1|S|3|T|5|U|7|21|8|@]|9|@]|A|$V|W]]|$1|X|3|Y|5|6|7|22|8|@]|9|@]|A|$]]|$1|Z|3|10|5|U|7|23|8|@]|9|@]|A|$V|W]]|$1|11|3|12|5|6|7|24|8|@]|9|@]|A|$]]|$1|13|3|14|5|U|7|25|8|@]|9|@]|A|$V|W]]|$1|15|3|16|5|6|7|26|8|@]|9|@]|A|$]]|$1|17|3|18|5|U|7|27|8|@]|9|@]|A|$V|W]]|$1|19|3|-4|5|6|7|28|8|@]|9|@]|A|$]]]|1A|$1B|$5|1C|1D|1E|A|$1F|1G|1H|-4]]|1I|$5|1C|1D|1E|A|$1F|1J|1H|-4]]]]

The provided answers are simply not true.
<a href="https://i.gyazo.com/1b3d863443e042e0b0012fcfc21e0573.png" rel="nofollow noreferrer"><img src="https://i.gyazo.com/1b3d863443e042e0b0012fcfc21e0573.png" alt="$ defined, no jQuery" /></a>
In this picture (taken on a Chrome <code>about:blank</code> tab), you can clearly see there is no jQuery. And given that the document is blank, there is no PrototypeJS as well. Contrary to all other answers, this is a native JavaScript function that can be used on any website.
The following picture shows the function definition.
<a href="https://i.stack.imgur.com/lZ19V.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/lZ19V.png" alt="$() definition" /></a>
<pre><code>ƒ $(selector, [startNode]) { [Command Line API] }
</code></pre>
If this isn't convincing enough, here's the function definition from jQuery:
<pre><code>ƒ (a,b) {return new n.fn.init(a,b)}
</code></pre>
Here is the function in PrototypeJS.
<pre><code>function $(element) {
 if (arguments.length &gt; 1) {
 for (var i = 0, elements = [], length = arguments.length; i &lt; length; i++)
 elements.push($(arguments[i]));
 return elements;
 }

 if (Object.isString(element))
 element = document.getElementById(element);
 return Element.extend(element);
 }
</code></pre>
I would disagree that this code is optimised appropriately, I would most certainly write it this way
<pre><code>function $(element) {
 if (arguments.length &gt; 1) {
 let elements = [];
 for (let i in arguments) elements.push($(arguments[i]));
 return elements;
 //or simply `return arguments;` without the loop and extra variable
 }
 return Object.isString(element) &amp;&amp; (e = document.getElementById(element)), Element.extend(element)
}
</code></pre>

What does the <code>$()</code> function do in the following example?

<pre><code>function test(){
 var b=$('btn1');
 eval(b);
}
</code></pre>

What does the $() function do in JavaScript?

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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在下面的示例中，$()函数的作用是什么？function test(){    var b=$('btn1');    eval(b);}

问$()函数在JavaScript中做什么？
EN

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问$()函数在JavaScript中做什么？EN