blocks|key|2752001|text|它对解释器没有任何意义，就像下划线一样|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2752002|来自ECMAScript规范：|2752003|2752004|标识符中的任意位置都允许使用美元符号($)和下划线(_)。美元符号仅用于机械生成的代码中。|blockquote|2752005|2752006|2752007|您也可以查看JavaScript+Dollar+Sign+($)+-+What+is+it+for?|offset|length|2752008|2752009|按照惯例，美元符号($)，下划线(_)甚至一些ASCII码字符都可以在JavaScript标识符中的任何地方使用(来源:+Ecma脚本文档(7.6标识符，ECMA-262，第三版))美元符号仅用于机械生成的代码。这意味着我们不想在标识符名中使用美元符号($)，除非我们正在编写框架。以下是可在标识符名称中的任何位置使用的允许字符的列表：|style|BOLD|2752010|2752011|2752012|IdentifierName+::
IdentifierStart
IdentifierName+IdentifierPart
IdentifierStart+::
UnicodeLetter
$
_
UnicodeEscapeSequence
IdentifierPart+::
IdentifierStart
UnicodeCombiningMark
UnicodeDigit
UnicodeConnectorPunctuation
UnicodeEscapeSequence|code-block|syntax|javascript|2752013|编辑：-|2752014|实际上，美元符号函数或多或少已经成为了document.getElementById()的事实上的捷径。|CODE|2752015|确认我的点数检查|2752016|选择器$(+|2752017|+)|2752018|2752019|返回与给定CSS选择器匹配的单个元素。在旧的Firebug版本中，这曾经等同于document.getElementById.|2752020|entityMap|0|LINK|mutability|MUTABLE|url|https://web.archive.org/web/20140318023849/http://www.authenticsociety.com/blog/JavaScript_DollarSign^0|0|0|0|0|0|0|6|18|0|0|0|2J|F|0|0|0|0|0|4|0|J|P|0|0|0|0|0|J|C|13|N|0^^$0|@$1|2|3|4|5|6|7|1L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1M|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|1N|8|@]|9|@]|A|$]]|$1|E|3|F|5|G|7|1O|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|1P|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|1Q|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|1R|8|@]|9|@$L|1S|M|1T|1|1U]]|A|$]]|$1|N|3|-4|5|6|7|1V|8|@]|9|@]|A|$]]|$1|O|3|P|5|G|7|1W|8|@$L|1X|M|1Y|Q|R]]|9|@]|A|$]]|$1|S|3|-4|5|6|7|1Z|8|@]|9|@]|A|$]]|$1|T|3|-4|5|6|7|20|8|@]|9|@]|A|$]]|$1|U|3|V|5|W|7|21|8|@]|9|@]|A|$X|Y]]|$1|Z|3|10|5|6|7|22|8|@$L|23|M|24|Q|R]]|9|@]|A|$]]|$1|11|3|12|5|6|7|25|8|@$L|26|M|27|Q|13]]|9|@]|A|$]]|$1|14|3|15|5|6|7|28|8|@]|9|@]|A|$]]|$1|16|3|17|5|6|7|29|8|@]|9|@]|A|$]]|$1|18|3|19|5|G|7|2A|8|@]|9|@]|A|$]]|$1|1A|3|-4|5|6|7|2B|8|@]|9|@]|A|$]]|$1|1B|3|1C|5|6|7|2C|8|@$L|2D|M|2E|Q|R]|$L|2F|M|2G|Q|R]]|9|@]|A|$]]|$1|1D|3|-4|5|6|7|2H|8|@]|9|@]|A|$]]]|1E|$1F|$5|1G|1H|1I|A|$1J|1K]]]]

It means nothing to the interpreter just like the underscore

From the ECMAScript specification:

<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.
</blockquote>

You may also check <a href="https://web.archive.org/web/20140318023849/http://www.authenticsociety.com/blog/JavaScript_DollarSign" rel="nofollow noreferrer">JavaScript Dollar Sign ($) - What is it for?</a>

<blockquote>
 By convention, the dollar sign ($), the underscore (_) and even some
 ASCII character are permitted to be used anywhere in a JavaScript
 identifier (Source: Ecma Script documentation (7.6 Identifiers,
 ECMA-262, 3rd Ed.) the dollar sign is intended for use only in
 mechanically generated code. This means that we do not want to use the
 dollar sign ($) in our indentifier names, unless we are writing a
 framework. The following is a list of permitted characters that can be
 used anywhere in an identifier name:
</blockquote>

<pre><code>IdentifierName ::
IdentifierStart
IdentifierName IdentifierPart
IdentifierStart ::
UnicodeLetter
$
_
UnicodeEscapeSequence
IdentifierPart ::
IdentifierStart
UnicodeCombiningMark
UnicodeDigit
UnicodeConnectorPunctuation
UnicodeEscapeSequence
</code></pre>

EDIT:-

Actually dollar sign function has become the more-or-less de facto shortcut to <code>document.getElementById()</code>.

To confirm my point check <a href="https://web.archive.org/web/20140330134536/http://getfirebug.com/wiki/index.php/Command_Line_API#.24.28selector.29" rel="nofollow noreferrer">this</a>:

<blockquote>
 $(selector)
 
 Returns a single element matching the given CSS selector. In old
 Firebug versions, this used to be equivalent to
 document.getElementById.
</blockquote>

blocks|key|2964613|text|它可以是任何东西，因为和dollar一样，$是一个有效的变量名。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2964614|来自ECMAScript：|2964615|Identifier+::
IdentifierName+but+not+ReservedWord

IdentifierName+::
IdentifierStart
IdentifierName+IdentifierPart

IdentifierStart+::
UnicodeLetter
$
_+
\+UnicodeEscapeSequence|code-block|syntax|javascript|2964616|要查看它是什么以及它是在哪里定义的，最简单的解决方案可能是在此行输入$()和put+a+breakpoint。|2964617|entityMap|0|LINK|mutability|MUTABLE|url|http://es5.github.io/#x7.6|1|https://developers.google.com/chrome-developer-tools/docs/javascript-debugging^0|C|6|L|1|0|2|A|0|0|0|Y|3|12|G|1|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|13|8|@]|D|@$9|14|A|15|1|16]]|E|$]]|$1|H|3|I|5|J|7|17|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|18|8|@$9|19|A|1A|B|C]]|D|@$9|1B|A|1C|1|1D]]|E|$]]|$1|O|3|-4|5|6|7|1E|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]|W|$5|R|S|T|E|$U|X]]]]

It may be anything, as <code>$</code> is a valid variable name, just like <code>dollar</code>.

From <a href="http://es5.github.io/#x7.6" rel="nofollow">ECMAScript</a> :

<pre><code>Identifier ::
IdentifierName but not ReservedWord

IdentifierName ::
IdentifierStart
IdentifierName IdentifierPart

IdentifierStart ::
UnicodeLetter
$
_ 
\ UnicodeEscapeSequence
</code></pre>

The simplest solution to see what it is and where it is defined would probably to type <code>$()</code> and to <a href="https://developers.google.com/chrome-developer-tools/docs/javascript-debugging" rel="nofollow">put a breakpoint</a> on this line.

blocks|key|2752251|text|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2752252|+1)几年前没有分配美元符号是正确的吗，还是我记错了？|blockquote|2752253|2752254|2752255|这是正确的，而且仍然是正确的。|2752256|2752257|+2)如果不是jQuery，那么美元符号是什么？|2752258|2752259|2752260|Firefox和Chrome将$、$$和其他几个实现为辅助命令。两者都会将$$设置为document.querySelectorAll()，如果尚未定义$，则将document.querySelector设置为window.$。|offset|length|style|CODE|2752261|因此，您看到的实际上不是标准的JavaScript，而是浏览器开发人员控制台中的帮助器。它也不是jQuery+(只要你不在使用jQuery的页面上)。然而，它的行为接近于jQuery的行为，因为querySelector+(对于单项匹配)和querySelectorAll+(对于多项匹配)为您提供了几乎与jQuery选择器相同的强度。|2752262|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Tools/Web_Console/The_command_line_interpreter#Helper_commands|1|https://developers.google.com/chrome-developer-tools/docs/commandline-api#selector^0|0|0|0|0|0|0|0|0|0|F|1|H|2|11|2|16|R|24|1|28|M|2X|8|0|7|0|8|6|1|0|2D|6|2P|D|3C|G|0^^$0|@$1|2|3|-4|4|5|6|14|7|@]|8|@]|9|$]]|$1|A|3|B|4|C|6|15|7|@]|8|@]|9|$]]|$1|D|3|-4|4|5|6|16|7|@]|8|@]|9|$]]|$1|E|3|-4|4|5|6|17|7|@]|8|@]|9|$]]|$1|F|3|G|4|5|6|18|7|@]|8|@]|9|$]]|$1|H|3|-4|4|5|6|19|7|@]|8|@]|9|$]]|$1|I|3|J|4|C|6|1A|7|@]|8|@]|9|$]]|$1|K|3|-4|4|5|6|1B|7|@]|8|@]|9|$]]|$1|L|3|-4|4|5|6|1C|7|@]|8|@]|9|$]]|$1|M|3|N|4|5|6|1D|7|@$O|1E|P|1F|Q|R]|$O|1G|P|1H|Q|R]|$O|1I|P|1J|Q|R]|$O|1K|P|1L|Q|R]|$O|1M|P|1N|Q|R]|$O|1O|P|1P|Q|R]|$O|1Q|P|1R|Q|R]]|8|@$O|1S|P|1T|1|1U]|$O|1V|P|1W|1|1X]]|9|$]]|$1|S|3|T|4|5|6|1Y|7|@$O|1Z|P|20|Q|R]|$O|21|P|22|Q|R]|$O|23|P|24|Q|R]]|8|@]|9|$]]|$1|U|3|-4|4|5|6|25|7|@]|8|@]|9|$]]]|V|$W|$4|X|Y|Z|9|$10|11]]|12|$4|X|Y|Z|9|$10|13]]]]

<blockquote>
 1) Is it correct that dollar sign was not assigned, a few years back, or do I remember wrong?
</blockquote>

That's correct and still true.

<blockquote>
 2) What is the dollar sign, if not jQuery?
</blockquote>

<a href="https://developer.mozilla.org/en-US/docs/Tools/Web_Console/The_command_line_interpreter#Helper_commands">Firefox</a> and <a href="https://developers.google.com/chrome-developer-tools/docs/commandline-api#selector">Chrome</a> implement <code>$</code>, <code>$$</code> and several others as helper commands. Both will set <code>$$</code> to <code>document.querySelectorAll()</code>, and set <code>$</code> to <code>document.querySelector</code> if <code>window.$</code> hasn't been defined.

So what you're seeing isn't actually standard JavaScript, but a helper in the developer console of your browser. It's also not jQuery (as long as you're not on a page using jQuery). However, it's behaviour is close to the one of <code>jQuery</code>, concerning that <code>querySelector</code> (for single matches) and <code>querySelectorAll</code> (for multiple matches) give you almost the same strength as the jQuery selector.

blocks|key|2964849|text|未分配Dollar+sign($)，但某些浏览器添加了特殊用途的功能。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2964850|和Google+Chrome一样，如果你在控制台上输入$，它会返回：|2964851|function+$(selector,+[startNode])+{+[Command+Line+API]+}|code-block|syntax|javascript|2964852|此函数分配给Google+Chrome开发人员工具，并让调试更容易。|2964853|如果您键入$('div')，它将返回如下内容：|2964854|e.fn.e.init[178]|2964855|并包含其中的每个div+DOM对象。|2964856|顺便说一句，在您单击鼠标右键选择元素之后，您可以通过在控制台上键入$scope来访问angular.js范围|2964857|entityMap^0|3|E|0|R|1|0|0|0|5|8|0|0|8|3|0|X|6|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|11|8|@$9|12|A|13|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|14|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|15|8|@]|D|@]|E|$]]|$1|O|3|P|5|6|7|16|8|@$9|17|A|18|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|J|7|19|8|@]|D|@]|E|$K|L]]|$1|S|3|T|5|6|7|1A|8|@$9|1B|A|1C|B|C]]|D|@]|E|$]]|$1|U|3|V|5|6|7|1D|8|@$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|W|3|-4|5|6|7|1G|8|@]|D|@]|E|$]]]|X|$]]

<code>Dollar sign($)</code> was not assigned, but some browser add function for special usage.

Like Google Chrome, if you type <code>$</code> on the console, it will return :

<pre><code>function $(selector, [startNode]) { [Command Line API] }
</code></pre>

This function assigned for Google Chrome Developer Tool, and let debug more easier.

if you type <code>$('div')</code>, it will return something like this:

<pre><code>e.fn.e.init[178]
</code></pre>

and include every <code>div</code> DOM object in it.

BTW, after you click the right button on the mouse to select element, you can acceess angular.js scope by type <code>$scope</code> on the console

blocks|key|159133|text|注意，$$并不完全是document.querySelectorAll，因为与该函数不同的是，它不返回NodeList|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|159134|document.querySelectorAll("p")+instanceof+NodeList+//+true

$$("p")+instanceof+NodeList+//+false

Array.isArray($$("p"))+//+true|code-block|syntax|javascript|159135|所以$$(selector)实际上更像Array.from(document.querySelectorAll(selector))。这意味着在使用$$时，可以使用像map和friends这样的数组方法，而不仅仅是forEach，这实际上非常有用。|159136|entityMap^0|3|2|A|P|1F|8|0|0|2|C|J|1B|22|2|2B|3|2Z|7|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]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|17|8|@]|D|@]|E|$]]]|N|$]]

Note that <code>$$</code> isn’t quite <code>document.querySelectorAll</code>, because unlike that function it doesn’t return a <code>NodeList</code>:
<pre class="lang-js prettyprint-override"><code>document.querySelectorAll(&quot;p&quot;) instanceof NodeList // true

$$(&quot;p&quot;) instanceof NodeList // false

Array.isArray($$(&quot;p&quot;)) // true
</code></pre>
So <code>$$(selector)</code> is really more like <code>Array.from(document.querySelectorAll(selector))</code>. This means that array methods like <code>map</code> and friends, not just <code>forEach</code>, are available when using <code>$$</code> which is actually quite useful.

blocks|key|2964871|text|为了完成这里的其他回答，MooTools还使用$作为document.getElementById的别名。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2964872|它会检查是否采用了$，然后将默认为document.id。|2964873|entityMap^0|N|1|Q|N|0|9|1|H|B|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|I|$]]

Just to complete the other answers here, MooTools also uses <code>$</code> as a alias to <code>document.getElementById</code>. 

It does check if the <code>$</code> is taken and will then default to <code>document.id</code>.

I did some javascript / jQuery programming a few years ago, and I just started up again. Back then the dollar sign was used for all the jQuery functionality, and if no jQuery library was imported, the dollar sign was not defined. 

Today, I started up Firefox, in a completely empty html file with no javascript libraries, and yet the dollar sign points to something. If I open the Firefox console and type '$' I get <code>"function()"</code>.

1) Is it correct that dollar sign was not assigned, a few years back, or do I remember wrong?

2) What is the dollar sign, if not jQuery?

What is the dollar sign in Javascript, if not jQuery

解释器

jQuery

几年前我做了一些javascript / jQuery编程，然后我又重新开始了。当时所有的jQuery功能都使用美元符号，如果没有导入jQuery库，就没有定义美元符号。今天，我在一个完全空的html文件中启动了Firefox，文件中没有javascript库，但是美元符号却指向了一些东西。如果我打开火狐控制台，输入'...

问如果不是jQuery，那么Javascript中的美元符号是什么
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