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The URL https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe... is also close to valid code as an expression.

Consider something like:

  foo ? https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/label
I was hoping that was where the post was going with this :)

Sadly, JavaScript doesn't have the // operator (floor division) so it doesn't quite work. And double-sadly, I can't think of a language that has all the necessary ingredients; Python uses `and` and `or` for trinary syntax, not ? and :, and besides, you'd need to be able to overload the // operator as unary rather than binary, which ... well, I'm not sure we'd want a language to be able to do that. But I do!

Still, if you want to confuse your coworkers, consider sneaking in something like:

  developer = {mozilla: 42}
  en = US = docs = web = Web = JavaScript = Reference = Statements = label = 420
  console.log(developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/label)
and be sure to hand in your resignation after pushing the commit.
For you young people, there is one language which is called "executable line noise".

This is valid Perl code syntactically, except Perl complains of invalid or incompatible regexp modifiers.

So, if you chose the characters carefully an url like that could be executable in Perl (but not this one or urls in general).

https://www.mcmillen.dev/sigbovik/: “93% of Paint Splatters are Valid Perl Programs”
I don't think you can make that or any URL into valid syntactic Perl code.

But maybe you're thinking of this - https://metacpan.org/pod/Acme::URL

  use Acme::URL;
  
  print https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/label;
Shouldn't that be :

  developer = {mozilla: {org: 42}} ?
`{mozilla: 42}` is enough because the goal is not to prevent NaN (arising from converting `(42).org` to a number).
Should work in Haskell. You can add your own operators there.
> Python uses `and` and `or` for trinary syntax

A nitpick: Python uses `if` and `else` for trinary syntax:

    a = foo if bar else baz
Scala can do it, except for // starting a comment, so it would have to be

    foo ? https:/developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/label
which of course isn't as cool. Still pretty close though.
everyone loves MDN, surely you should only resign after commiting w3schools?
> The lowdown: you can copy and paste just about any website directly into your JavaScript code without modification and it won't break anything.

Well, unless your code relies on an `http` or `https` label :)

And it also won't work between member declarations of a class. Basically it only works where statements are legal.
One also could look at it the other way around: an URL always matches any string, that includes Javascript code. Here is a nice example from the real world:

Whenever I use the Regex engine of XML Schema (or later XPath), with the regular expression shown in RFC3986 - Uniform Resource Identifier (URI): Generic Syntax, I get the error: "Regular expression matches any string.". (The reason for this being an error is, that the XSD regex engine had only one purpose: to constrain a string, so we can check for valid input or define a datatype. That's why it behaves that way.) Here is the part with the regex from Appendix B[1] of aforementioned RFC:

    The following line is the regular expression for breaking-down a
    well-formed URI reference into its components.

        ^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))?
         12            3  4          5       6  7        8 9

    The numbers in the second line above are only to assist readability;
    they indicate the reference points for each subexpression (i.e., each
    paired parenthesis).  We refer to the value matched for subexpression
    <n> as $<n>.  For example, matching the above expression to

      http://www.ics.uci.edu/pub/ietf/uri/#Related

    results in the following subexpression matches:

      $1 = http:
      $2 = http
      $3 = //www.ics.uci.edu
      $4 = www.ics.uci.edu
      $5 = /pub/ietf/uri/
      $6 = <undefined>
      $7 = <undefined>
      $8 = #Related
      $9 = Related

    where <undefined> indicates that the component is not present, as is
    the case for the query component in the above example.  Therefore, we
    can determine the value of the five components as

      scheme    = $2
      authority = $4
      path      = $5
      query     = $7
      fragment  = $9
[1]: https://datatracker.ietf.org/doc/html/rfc3986#appendix-B
Not exactly. The original URI syntax didn't allow several characters including "{|`><}\^ plus whitespaces anywhere; the quoted section of RFC 3986 assumes that the string is already well-formed (thus the regex can't be used for the validation). Even the modern URL Standard has an outright failure [1].

[1] https://url.spec.whatwg.org/#example-url-parsing

Semi-related, there's a a useful trick for using Javascript labels as URLs.

Way back in the day, I used to write labels like `<a href="javascript:open_save_dialog:;">` instead of `<a href="javascript:void(0)">`. The idea is that both yield undefined to prevent the default URL following semantics of the link, to instead do whatever JS logic is attached to the onclick event, but when the user hovers over the link, the label makes the corner tooltip of the browser show descriptive information to the user about what clicking will do, whereas `void(0)` tells you nothing.

Remove the protocol part, and with the JS Proxy[0], you can actually do something like:

  await www.example.org
as demonstrated in a tweet[1]. This is pretty interesting IMO :-)

[0]: http://developer.mozilla.org/en-US/docs/Web/JavaScript/Refer...

[1]: https://twitter.com/rreverser/status/1138788910975397888

And in Rebol & Red URL's are syntactically valid datatypes (literals): http://www.rebol.com/r3/docs/datatypes/url.html

For eg. in Red console:

    >> read https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/label
    
    == {<!DOCTYPE html><html lang="en-US" prefix="og: https://ogp.me/ns#"><head><me...
I want this. Esp in DSLs. Bonus points for first class support for fragments and so forth.

(aka Intrinsics?)

Whenever I come back to writing JavaScript after a long break, I always forget how to correctly return objects from lambda expressions, and end up with this:

    () => {
       foo: "bar";
       baz: "qux";
    }
Thankfully TypeScript warns me it's a ()=>void function instead of whatever was expected in the context. I scratch my head for a while and then remember:

    () => ({
        foo: "bar",
        baz: "qux"
    });
I'm more baffled that

    foo: "bar";
is a valid expression. I know, it's the named statement syntax normally used for loops, but I didn't know this worked for any expression.
No different than Java or any lang that supports labels and c style comments
Technically it's C++-style comments, the original C only had /* */ comment blocks.
At some point in the distant past I was working on a tool that would identify PowerShell script using the built in parsing API. It was astonishing the wide variety of files that parsed without error, including a lot of XML files.
You really should not use this ever in any situation, but for historical reasons[1], if they are the only thing on the line you can use HTML comments in JavaScript like so:

  function foo() {
    <!--- returns true ---->
    return true;
  }
This works at least in Chrome and V8, not sure about Firefox.

[1] https://stackoverflow.com/a/1508005/1888964

So even a data URI can be valid JS syntax

  data:document/document,alert('hi')
If ran as JS it will alert "hi". If put into a link it will force the browser to download a document containing the alert statement.
That data URI happens to use `document` which happens to be a browser global, so most data URIs won't work.

e.g. running the above in Node gives:

  Uncaught ReferenceError: document is not defined
For anyone unfamiliar with JS, the above string is parsed as:

  (label):
    (variable cast to int) / (variable cast to int), // evals to NaN
    (function call) // evals
I was actually not aware that JavaScript supports labels. Quite funny since, usually, these articles are about quirks in JS that basically no other language has.
This is a neat trick, but I'm more interested in the little remark about how Svelte uses the $: label

https://svelte.dev/docs#3_$_marks_a_statement_as_reactive

Is Svelte doing something clever with these labels at runtime, or is it just using the label to do some kind of transformation when the javascript is compiled, anyone know?

I believe it's parsing the JavaScript and doing a transformation. That's kind of svelte's USP: better ergonomics because it goes beyonds what's possible in standard JS.
> The lowdown: you can copy and paste just about any website directly into your JavaScript code without modification and it won't break anything.

The following doesn't seem to be valid though. :( Am I missing something?

    https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/label

    let a = 1;
Sort of the same reason why `if (true) let a = 1` is a syntax error (and the error message says why: "Lexical declaration cannot appear in a single-statement context")

The rationale here is that the variable goes out of scope right away due to the implicit block, so they made it a syntax error so that you don't waste time pulling your hair out debugging issues downstream from this line without realizing this scope-related obscurity. (This also has potential security implications e.g. if you think you're shadowing a variable from a parent scope but you're not)

```

>> https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

10

<- 10

```

Eg, this is equivalent to:

```

>> https: 10

```

I can remember putting the URL of the Matrix movie website, in some plain Java code that dealt with well, matrices.

What I did not know is my code was more or less secretly reviewed by a senior engineer, who was a bit surprised, but learnt something he told me.

This is how the secret review became public. My red pill, indeed!

edit: typo

C# too
C too, C++ too
Neat, but as TFA says, not useful.

Objective-S makes URIs useful: http://objective.st/URIs/

    Unused label.ts (7028)
    'https:' is defined but never used. (eslintno-unused-labels)
    Delete `https:` (eslintprettier/prettier)
Awesome! It's basically a label either https: or http: that gets nothing assigned to it since the // turns everything afterwards into a comment.
one of my earliest programming qirk encounters was scratching my head over why `() => { key: value }` returns nothing
Nix has first-class support for URLs. Like, there are strings ("https://example.org") and URLS (https://example.org). And if URL is not valid, it will be parser error.

However, this "feature" turned out to be misfeature and may be removed in future.

The RFC: https://github.com/NixOS/rfcs/blob/master/rfcs/0045-deprecat...

javascript delenda est
Javascriptus delenda est.

Or: Ceterum autem censeo Javascriptum esse delendam.

I wanted to read this, but the styling of the website cuts diagonally across the content on my tablet in portrait mode.

It makes the article unreadable...

Punchline, http: is a label; // and everything following is a comment.
Yes, but do you know how long it took us to get CSS to this stage so that it could draw arbitrary shapes???