Defensive programming benefit of the bang method ("!") is not correct.

First off this is a great document, and thanks for sharing it. I have read the entire file end-to-end as I work on my own personal style guide. However, I was looking at your module example and you assert that “!” protects you from concatenation errors. However, I don’t think this is correct. Consider the following example:

// => SyntaxError: Unexpected token !
!function(){console.log("ham");}()!function(){console.log("cheese")}();

Maybe I am misunderstanding how you expected things to work.

I think you still need to prepend a semicolon to truly protect yourself from concatenation errors.

;!function(){console.log("ham");}()

[reissbaker]

You would have to prepend a semicolon… If the cat command concatenated files together that way. Fortunately, though, it doesn’t:

$ cat ham.js cheese.js
> !function(){console.log("ham");}()
> !function(){console.log("cheese");}();

The cat command (and *nix-land concatenation in general) concatenates files onto separate lines. That’s why bang modules work: the ! at the start of the line allows Javascript ASI to kick in on the previous line and insert any missing semicolons for you. As proof, try evaluating the following in the console:

!function(){console.log("ham");}() // Missing semicolon!
!function(){console.log("cheese");}();

As you can see, there’s no TypeError. The only similarly safe equivalent in the traditional module-land is ;(function(){}());, which is just silly.

I can’t speak for file concatenation in Windows environments — all I can say is we don’t use them for deployment at Airbnb, and so we don’t worry about their behavior. My hunch is things work the same way over there too, though.

[hshoff]

Thanks for the discussion, this was a good read! 🍻