My mind was completely blown when my coworker showed me this JavaScript code that alerts 42.
alert(2+ 40);I soon discovered that the seemingly negative sign is actually a mysterious Unicode character with unique functions.
This discovery led me to question why this character doesn't trigger a syntax error during parsing. It made me curious about whether there are other characters out there with similar behavior.
That particular character identified as "OGHAM SPACE MARK", serves as a space character. Hence, the code can be simplified to alert(2+ 40).
I am curious if there are other characters that exhibit this behavior.
In JavaScript, any Unicode character categorized under the Zs class is recognized as a white space character according to standards. As of now there don't appear to be many such characters.
Additionally, JavaScript has provisions for using Unicode characters in identifiers, enabling the use of intriguing variable names like ಠ_ಠ.
After reviewing the responses provided, I developed a straightforward program to identify all Unicode characters within the range U+0000–U+FFFF that act as white spaces. It appears that there are approximately 26 or 27 such characters, with discrepancies surrounding U+0085 and U+FFFE.
It is important to note that many of these characters simply resemble a standard white space.
function isSpace(ch)
{
try
{
return Function('return 2 +' + ch + ' 2')() === 4;
}
catch(e)
{
return false;
}
}
for (var i = 0; i <= 0xffff; ++i)
{
var ch = String.fromCharCode(i);
if (isSpace(ch))
{
document.body.appendChild(document.createElement('DIV')).textContent = 'U+' + ('000' + i.toString(16).toUpperCase()).slice(-4) + ' "' + ch + '"';
}
}div { font-family: monospace; }It seems that the character you are using is longer than the minus sign (hyphen).
-
The top shows what you're using, the bottom shows the correct minus sign. You already know this, so let's explore why Javascript behaves this way.
The character you're using is actually the ogham space mark, a whitespace character interpreted as a space by Javascript. So your statement looks like alert(2+ 40) to Javascript.
Javascript has other characters like this; see a full list here on Wikipedia.
I noticed an interesting behavior of this character in Google Chrome and possibly other browsers' address bars.
The bar displays a block with 1680 inside - the unicode number for the ogham space mark. It might just be my machine, but it's peculiar.
I tested this in various languages with these results:
Python 2 & 3
>> 2+ 40
File "<stdin>", line 1
2+ 40
^
SyntaxError: invalid character in identifier
Ruby
>> 2+ 40
NameError: undefined local variable or method ` 40' for main:Object
from (irb):1
from /home/michaelpri/.rbenv/versions/2.2.2/bin/irb:11:in `<main>'
Java (inside the main method)
>> System.out.println(2+ 40);
Main.java:3: error: illegal character: \5760
System.out.println(2+?40);
^
Main.java:3: error: ';' expected
System.out.println(2+?40);
^
Main.java:3: error: illegal start of expression
System.out.println(2+?40);
^
3 errors
PHP
>> 2+ 40;
Use of undefined constant 40 - assumed ' 40' :1
C
>> 2+ 40
main.c:1:1: error: expected identifier or '(' before numeric constant
2+ 40
^
main.c:1:1: error: stray '\341' in program
main.c:1:1: error: stray '\232' in program
main.c:1:1: error: stray '\200' in program
exit status 1
Go
>> 2+ 40
can't load package: package .:
main.go:1:1: expected 'package', found 'INT' 2
main.go:1:3: illegal character U+1680
exit status 1
Perl 5
>> perl -e'2+ 40'
Unrecognized character \xE1; marked by <-- HERE after 2+<-- HERE near column 3 at -e line 1.
Scheme
>> (+ 2 40)
=> 42
C# (inside the Main() method)
Console.WriteLine(2+ 40);
Output: 42
Perl 6
>> ./perl6 -e'say 2+ 40'
42
It seems like the reason for this behavior has something to do with how it is classified as whitespace:
$ unicode
U+1680 OGHAM SPACE MARK
UTF-8: e1 9a 80 UTF-16BE: 1680 Decimal:  
( )
Uppercase: U+1680
Category: Zs (Separator, Space)
Bidi: WS (Whitespace)
I would like to know if there are other characters who exhibit similar behavior.
I recall coming across an article that talked about replacing semi-colons (U+003B) with the Greek question mark (U+037E) as a mischievous prank in someone's code.
Although both characters look identical (so much so that even Greeks use U+003B), the article mentioned that one of them does not function the same way.
You can find more information on this topic on Wikipedia here: https://en.wikipedia.org/wiki/Question_mark#Greek_question_mark
There is also a closed question on using this prank on Stack Overflow, although that wasn't where I originally read about it: JavaScript Prank / Joke
When it comes to compiling this expression, most languages shy away. However, my curiosity led me to test Rust's compiler on the matter. Known for its strictness, Rust often imparts knowledge and wisdom in a gentle manner.
So I decided to see how it would handle this:
fn main() {
println!("{}", (2+ 40));
}
And here is what the compiler had to say:
error: unknown start of token: \u{1680}
|
| println!("{}", (2+ 40));
| ^
|
help: Unicode character ' ' (Ogham Space mark) looks like ' ' (Space), but it is not
In contrast, JavaScript (tested with the latest and most commonly used browser today) appears to be more lenient towards that character, simply ignoring it.
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