Javascript function declarations with a dollar sign

Question

This function declaration doesn't make sense to me. What does the $ sign do?

function $(id) { return document.getElementById(id); }

Also, this code is interfering with other Javascript code. If I comment it out, then the other Javascript code I'm trying to use works, but then I lose some other functionality.

Why might it be interfering with my other code.

[What is the meaning of “$” sign in javascript](http://stackoverflow.com/questions/1150381/what-is-the-meaning-of-sign-in-javascript) — , Jan 26 '12 at 23:28

score 4 · Answer 1 · answered Jan 26 '12 at 23:20

What does the $ sign do?

Nothing special. It is just a character that can be used in variable/function names.

There has been a trend to use $ as the name to the gateway function for a number of libraries (including Mootools, Prototype and jQuery). This has two major problems:

It makes them conflict with each other
It violates the principles of self-documenting code

Also, this code is interfering with other Javascript code.

Presumably something else is using a variable called $ then.

score 3 · Accepted Answer · edited May 23 '17 at 12:30

3

You are declaring a function called $ that wraps document.getElementById, apparently for convenience. Nothing special.

Reference What characters are valid for JavaScript variable names?

As for the interference, there is likely another global variable called $, which is being clobbered. See jQuery.

edited May 23 '17 at 12:30

Community

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answered Jan 26 '12 at 23:21

calebds

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Yes, jQuery is being used. So how can I change this variable so that the conflict goes away? – node ninja Jan 26 '12 at 23:33
@javascriptninja rename the function to something unique. It will be difficult to determine where _that_ function is being called tho, so you can update.. – calebds Jan 26 '12 at 23:34

alex · Answer 3 · 2012-01-26T23:27:54.843

JavaScript variables can start (and only consist of) a $ (amongst others).

Previously, the $ was added solely for machine generated variables.

This was in the spec I believe, but has since been removed (don't quote me).

Dollar sign was added to the language specifically for use by code generators and macro processes, so if you have machines writing code then the machines need to be confident that the variables that they create will not conflict with variables that the humans are going to create. To distinguish them, we’ll allow the machines to use dollar sign. Some of the ninjas found out about that and thought oh, dollar sign, I can use dollar sign as a function name, so they’re out there doing that. And it looks stupid. I mean, look at a program with dollar sign.

Source: Douglas Crockford.

If it is interfering with other code, you may be using a library which uses this identifier. If that's the case, look at the no conflict mode for that library (if it has one).

score 1 · Answer 4 · answered Jan 26 '12 at 23:21

Let me guess: are you using jQuery or prototype?

$ and _ are valid characters in variable/function names. The code is the same as declaring function a(id) {return document.getElementById(id);}.

It's typically used as a shortcut for selecting an element because typing document.getElementById is much too long for how often it's used.

Javascript function declarations with a dollar sign

4 Answers4