What is the hash tag used for in JavaScript?

Question

I'm not talking about in the URL. I know what that does. I'm talking about how it's used in actual code.

After trying to assign it as a variable, I realized that it's reserved, but I don't know what for.

So you're trying to do `var # = "foo"` and # is reserved? – Surreal Dreams Mar 08 '11 at 15:43 — Surreal Dreams, Mar 08 '11 at 15:43
Could you specify what you mean? – Johannes Fahrenkrug Mar 08 '11 at 15:50 — Johannes Fahrenkrug, Mar 08 '11 at 15:50

thabs · Answer 1 · 2022-06-30T08:35:16.760

2

An ongoing proposal (currently in stage 4) utilizes hashtags to mark fields as private. It is part of the ES2022 standard.

Example:

class Foo {
  x = 1; // public field
  #y = 2; // private field

  add() {
    return this.x + this.#y;
  }
}

edited Jun 30 '22 at 08:35

answered Jun 30 '22 at 08:28

thabs

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score 1 · Answer 2 · answered Mar 08 '11 at 15:47

I dont think, that this sign is somehow reserved fot another functionality. I found that rule here:

You must not use any punctuation marks of any kind in a JavaScript variable name, other than the underscore; for example... some:thing or big# or do'to would all be illegal.

This ist just, that javascript does not accept punctation signs in variable names ant due to this not parsing variables named like this as variables.

score 1 · Accepted Answer · answered Mar 08 '11 at 15:48

1

Javascript, or more precisely ECMAscript, is an evolving language. Some symbols and keywords (such as "class") have been reserved for future versions, even though they may not have any meaning at the moment.

answered Mar 08 '11 at 15:48

Bart

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It's worth noting that `#` is the prefix for private attributes in ES6. – bitsmanent Jun 13 '19 at 13:32

score 1 · Answer 4 · edited May 23 '17 at 12:11

1

See here: What characters are valid for JavaScript variable names?

edited May 23 '17 at 12:11

Community

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answered Mar 08 '11 at 15:56

Johannes Fahrenkrug

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Surreal Dreams · Answer 5 · 2011-03-08T17:24:17.363

0

In JavaScript variable names, no punctuation marks are permitted except for the underscore (_) and dollar sign ($). You can't start a variable name with a number, but otherwise all letters and numbers are permitted in a variable name.

So you can't have a variable name with # in it, no less a variable named #. It has no special meaning, it's just not permitted just as variable can't be named ~.

edited Mar 08 '11 at 17:24

answered Mar 08 '11 at 15:48

Surreal Dreams

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The $ sign is also a valid character for a variable name. – Johannes Fahrenkrug Mar 08 '11 at 15:55

What is the hash tag used for in JavaScript?

5 Answers5