That character is “OGHAM SPACE MARK”, which is a space character. So the code is equivalent to alert(2+ 40).
I’d also like to know if there are more characters behaving like this.
Any Unicode character in the Zs class is a white space character in JavaScript, but there don’t seem to be that many.
However, JavaScript also allows Unicode characters in identifiers, which lets you use interesting variable names like ಠ_ಠ.