"ASI [“Automatic Semicolon Insertion”] is an error correction
procedure. If you start to code as if it were a universal
significant-newline rule, you will get into trouble."—Brendan Eich<a onClick = "someFunc()" > ...
> Error, missing semicolon after ")" on line 1
That could get pretty annoying pretty fast, and simple little event handlers like these were probably the main use of JavaScript for the first x years. It also matched the existing philosophy of HTML which was to really go out of its way to make sense of whatever was in the file.
Now of course, the constraints are different: people want to use JavaScript for huge codebases and serious projects, so it makes sense that these decisions are no longer appropriate.
Depends whether the semicolon is defined as a terminator or as a separator.
This would be valid code with statement separator semicolons.
If you try to take your key with you at all times, the super will save your bacon once in a blue moon when you forget your key. On the other hand, if you think of the door as only needing a key when you wish to have it opened on nights and week-ends, you are on your way to trouble.
As usual, analogies do more harm than good, especially when understanding a relatively simple technical issue.
On another topic, this isn’t really a technical issue, it’s a people issue. Everyone understands what the JS interpreter’s behaviour is, what Bootstrap.js does, and why JSMin doesn’t minify it. What is being discussed here is what choices people make to please themselves and others as opposed to the compiler.
If @fat didn’t care about people, he’d use semicolons and JSMin would compile Bootstrap. If Crockford didn’t care about people, JSMin would compile Bootstrap just the way it is. When we’re talking about multiple ways of writing code that does the same thing, it’s almost entirely about people and not technical considerations.
But you don't need analogies to understand why ASI is a bad idea. ASI means that when you leave out a semi-colon you get unexpected behavior instead of a syntax error. Failure is always better than the unknown. At least then there's a chance the bug will be found and fixed.
Proceeds to offer an even worse analogy. Good one :)
ASI is supposed to work in exceptional scenarios where you would have ended up making a mistake but wouldn't want to be reminded of. And that is supposed to be in rare scenarios.
Now if you make exception the norm and expect tools to make up for bad practices then its not going to help.
And this is why I think Python's forced indentation is in some way bad. Because it makes the code from a bad and good programmer both look same. And merely forcing code indentation won't magically transmogrify a bad programmer to a good programmer. There are many things to good programming and indentation is just one of them. Worse it will make both's code look the same.
Forgiving or masking or making bad practices look good doesn't help on the longer run. It only encourages such behavior. I am sure bad programmers can slip in easily into these communities than else where, because they are difficult to flush out and their mistakes are often forgiven or made look good.
"ASI is (formally speaking) a syntactic error correction procedure."
Yet the "expectation of ASI" or (I think more likely) "expectation of newline significance" makes people believe that they'll get a ; inserted by separating two things by one or more newlines.
Most languages do not specify error correction. HTML5 of course does; CSS too; among general programming languages it's much less common. The spec for ASI does not fit in the tried-and-true LR(1) formalism used by ECMA-262. Parsing is not all ad-hoc or equally well-formalized and proven.
In addition to ASI, ECMA-262 has to use lookahead restrictions and a bit of semantic checking to cope with what could be purely syntactic concerns (say, if it could use GLR instead of LR(1)).
The error-correction view seems to want to add a third category, strings that are in some sense "errors", but nonetheless get unambiguously mapped to an AST. Which is strange from a classical formal-languages view, because if a string gets mapped to an AST, it's in the language, and the procedure that mapped it constitutes the parser! That category seems more like "warnings" to me, i.e. you probably shouldn't do this, but it will produce a program if you do.
But that doesn't alter ASI's error-correction nature, which is not an "implementation detail" -- it's in the spec and all too observable.
You're right, it has the character of a warning system, like Dart's unsound "types". But if it had been noisy (consoles in the early days were costly), too many developers would have ignored the warnings, and users would have paid for the overhead.
Your concluding sentence is spot on, I agree people should use semicolons in JS. Relying on a Ruby-like coding style in the large is way too risky.
Perhaps I've worked too much in teams, but surely "path of least resistance" has to factor some, right? I mean, if the choice is add a semi-colon to a line in a file versus asking somebody else to rewrite the compiler to be able to accept it, surely common sense would just be to add the semi-colon.
It doesn't mean that you're wrong, or that your code is broken, or that Crockford is smarter than you... but now you have code that works and compiles and that people can use.
Surely, that's gotta count for something, right?
Sure it is the easier solution right now. But in the long run that would mean the Crockford would be able to dictate the style of Javascript to whatever the hell he wants.
Given how important Javascript is now (and will be in the future) we cannot allow any one person to retard the entire future.
Anyway use Googles closure compiler -- it can actually handle Javascript.
So long as he keeps building tools and utilities that people rely on, and that people use, he is at least influencing the direction of Javascript and, knowing that, I'd think one might take heed when Crockford says "this will break in the future", as he happens to have more insight into the language than most.
I understand that he wasn't polite, and I certainly understand the desire for the 'asshole' to be proven wrong. And maybe he is. Of course, that doesn't make him wrong, and it doesn't mean that he's "retarding the future" either, necessarily.
But the fact that jsmin is perhaps the most widely deployed JS minification utility does matter, whether anyone chooses to accept it or not.
And if you really think that he is retarding the future, the correct answer probably isn't to bicker about it on the internet, but to create a better compiler (or work on getting a better compiler accepted) as de facto.
At the end of the day though, Fat is the guy who has to deal with all the tickets talking about 'This doesn't compile in jsmin', and I'd think his life would ultimately be better off if he just added a semi-colon.
Of course, that's my opinion only, so take it for what it's worth.
Doug may have forgotten the [no LineTerminator here] restriction, or he may not want it to the left of infix-! for promises, but I am certain that the whole of TC39 will not agree to such a breaking change.