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I am starting to love jQuery but as PHP developer I hate using that 

$().stuff

as everyone know $ in PHP marks variables. I guess jQuery in javascript declares a function like this

function $(element) {/*stuff*/}

Does javascripts permits $ as the name of a func? Is that a good behaviour?

I knew only standard [0-9a-zA-Z_] could be the name of funcs/vars.

Am I missing something?

Thanks

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  • how can i make this question CW Commented Mar 19, 2011 at 13:15
  • Nothing like checking the spec: ecma-international.org/publications/standards/Ecma-262.htm (Section 7.6). Identifiers can consist of one or more of any unicode character, specifically including $ and _. Commented Mar 19, 2011 at 13:16
  • @yes123: "how can i make this question CW" If you click edit, there may be a "Community Wiki" checkbox under the question box. If there is, tick it and click Save Edits. If not, you don't have enough rep yet to make it a CW after the fact (you could when originally asking the question). Commented Mar 19, 2011 at 13:18
  • @T. J. Crowder it's not really any unicode character; there's (apparently) a Unicode "identifier" concept and that's what Javascript follows, so identifiers can have all sorts of crazy things but not spaces or commas etc ... Commented Mar 19, 2011 at 13:21
  • @crow: ok i will stick with normal question Commented Mar 19, 2011 at 13:21

5 Answers 5

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The use of $ in PHP was a flat-out mistake, which was also made by the inventor of Perl. Variable prefixes are redundant in a full-fledged computer language because identifiers like foo and bar can be assumed to be variables without qualification — what else would an identifier be identifying? :-) The problem is that the amateurs who invented these languages were very familiar with the Unix shell, and they apparently did not realize that the $ that goes in front of shell variable references like $PATH is not a beautiful language feature, but an ugly necessity imposed by the fact that, in a shell script, words can appear normally “as themselves”, as when you say:

$ echo PATH
PATH
$ echo $PATH
/usr/local/bin:/usr/bin:/bin

In other words, an escape character like $ that says “this is a variable!” is necessary in a text substitution language like the shell, and escaping is also important in things like TCL and, of course, in modern templating languages, where you have to be able to tell apart all of the normal text that should be copied into the web page apart from the variable references and loops that pull in dynamic information.

But normal programming languages do not work by text substitution, so the $ in Perl and PHP is cruft and noise.

Since $ has no other use in JavaScript, it was a simple aesthetic judgement about whether to make it available as a “normal letter” for variables. JavaScript said “yes”, Python said “no”, and I have gotten used to both choices. I guess it now “looks like JavaScript” to me for $ to be valid!

But in no case should you let your aesthetic judgement here be informed by the horrible choices of Perl and PHP, which were wrong choices! Instead, ask yourself whether $ looks enough like a capital S that you can consider it to be “close enough to a letter”, or whether it looks forever like a symbol to you. That's the real choice.

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6 Comments

I think Brandon is right. The only place it can be confusing in javascript is when you use $1, $2 etc for variable names (valid, but also used as placeholders with regular expressions).
$ in PHP is not a prefix. It's a function itself that takes whatever is right to it and resolves the value of the variable with that name. That's also why $$test and so on work.
@Ivo — thank you for pointing out that the $ is not simply syntactic, but names something. My point, however, still stands: PHP decided to put the most natural thing in the world — local variables — “one step away” from what can simply be named without qualification.
The PHP is a template language. You can write something like: echo "The name of my cat is $cat_name.";. It is possible to use strings without quotes in few situations too. However, this is deprecated.
@Michas — I have no objection to special characters like $ in an inline template string — they are, as you point out, obviously necessary to mark cat_name as a variable while name, of, and cat are not variables. My objection is to carrying this template noise into the language itself, in its own expressions, outside of quotation marks.
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From the MDC docs:

A JavaScript identifier must start with a letter, underscore (_), or dollar sign ($); subsequent characters can also be digits (0-9). Because JavaScript is case sensitive, letters include the characters "A" through "Z" (uppercase) and the characters "a" through "z" (lowercase).

I think the key concept here is that, in Javascript, functions are first-class. This means that they are objects, just like everything else. The name you use to refer to a function is effectively a variable.

So, as an example, you can do this:

var myFunc = function() { /* some code */ };

and then call the function as myFunc().

Since $ is a valid character in identifier names, it is a valid name for a function just as much as a variable containing anything else.

In my opinion, the use of $ as a sigil for every variable in PHP is bone-headed.

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-1 isn't bone-headed, it's perfectly fine especially when you are doing something like this "Value of name is {$name}" for example.
+1 Good call posting MDC docs and linking them! :) I agree that PHP is boneheaded in its use of $. But I think PHP is boneheaded in large portions of what it does!
@yes123, that's kinda messed up to down vote that answer because of one point with which you disagree. The info given answers your question quite well and quotes an authority on the matter.
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Yes, it's valid. Crockford hates it, others love it. If you don't like it, don't use '$', use 'jQuery'. You can even put jQuery into no conflict mode so that $ never gets set. That said, if you're writing enough JS via PHP that it's causing you problems, you should probably consider learning how to write better, more generic JS.

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indeed I use jQuery, but typing evertime jQuery isn't fun,
@yes123: Use anything you want: var foo = jQuery.noConflict(); or if you use the ready function or its shortcut, you can take your desired symbol as a parameter: jQuery(function(foo) { foo("div").css("color", "red"); }); More: api.jquery.com/jQuery.noConflict
@jaalude I don't have any problems with writing php + js, it just something related to "habits" -1
Thanks for adding that bit about noConflict's return value. I neglected to mention it, and it is helpful to the situation.
@yes123, you've got some crappy Stack Overflow manners. Stop down voting people's perfectly valid answers simply because you don't like an opinion offered therein. The opinion isn't the answer, it's some added conversation on the matter.
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Javascript just allows more then just a-z for function names. $ is a valid name for a function and $ has no special meaning like in php. So $ is a correct name for a function.

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You can do

var whatever = $.noConflict();

now you can use whatever(..) instead of $(...)

documentation at http://api.jquery.com/jQuery.noConflict/

and quoting Values, Variables, and Literals

A JavaScript identifier must start with a letter, underscore (_), or dollar sign ($); subsequent characters can also be digits (0-9).

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Excellent point about noConflict's return value. I neglected to mention it, and it is helpful to the situation.