Why are programmers afraid of not using semicolons in JavaScript?

http://programmers.stackexchange.com/questions/99195/why-are-programmers-afraid-of-not-using-semicolons-in-javascript-but-dont-care-i

by einaregilsson • 15 years ago

36 69 15 years ago

programmers.stackexchange.com

evilswan• 15 years ago

"...but you have to be aware of some edge cases"

There's the reason.

bryanlarsen• 15 years ago

The point of the article is that Python has very similar edge cases yet nobody advocates the use of semicolons in Python.

veyron• 15 years ago

Because python handles them in a way that people would expect python to handle them

einaregilsson12• 15 years ago

But isn't that part of learning any language? There are plenty of weird edge cases in other languages but we get used to them. Basically this boils down to:

"When you have a single statement, that stretches out over more than one line, but those lines are legal statements on their own, then it won't work like you want it to"

I would guess that the number of statements that stretch out over many lines are a very small part of the overall number of statements for most code.

But it just seems like most developers think that javascript might insert semicolons all over the place. Which it won't, the rules are clear once you learn them.

einaregilsson12• 15 years ago

Ahem, maybe not as clear as I thought, since I found a few other edge cases I didn't know of in this excellent article:

Best article I've read on the subject: http://inimino.org/~inimino/blog/javascript_semicolons

felipemnoa2• 15 years ago

Or, just add a semicolon and keep it simple. Why risk it? KISS at work.

sjs9• 15 years ago

Isn't it really only one edge case, that being punctuation at the beginning of a line?

drivebyacct2• 15 years ago

But using semicolons doesn't eliminate those edge cases. Those are just places where auto-semicolon-insert fails to standup to what humans perceive to be the "right" behavior. Semicolons or no, if you put a newline character between return and the retval, you will get the "wrong" behavior.

snorkel2• 15 years ago

Force of habit and clarity. Sometimes it's necessary, like "return i++" is ambiguous.

einaregilsson12• 15 years ago

return i++ is not ambigous. It will return the current value of i, e.g. if i was 2 it will return 2, not 3. But that's just how the post increment operator works (in every language that I know of), that has nothing to do with semicolon insertion.

eropple3• 15 years ago

"return i++" is not ambiguous, on that you are correct--but it is terrible practice because it lends itself to being misconstrued.

Writing clear code is superior to writing "cute" code, and "return i++" is a case of the latter. In any case where the increment actually matters you are directly affecting a shared state and such changes should be made contextually obvious to the state of the object--one's neck would need to be very, very beard to think that this is immediately obvious and apparent in a contextually valid way.

Similarly, for many programmers, myself included, a semicolon is read as a period is in English--the end of the statement. (You keep saying that "but people don't get annoyed at Python when it does it," and guess what? I certainly get annoyed at it--Python consistently frustrates me because I find it considerably less readable.) Omitting semicolons is less immediately clear than including them and, again, can be misconstrued. Only it can be misconstrued by the program interpreter, too. (Oops.)

snorkel2• 15 years ago

It is ambiguous when the coder intended to return directly without returning any value like so:

    while (word = getNextWord()) {
      doSomething(word)
      if (i > limit) return
      i++
    }

Sure, this can be written better but a semi-colon after "return" makes it less ambiguous.

jannes• 15 years ago

There are some caveats. This, for example, would not work as expected:

  foo()
  [1,2,3].forEach(bar)

Automatic semicolon insertion wouldn't work here, because the bracket could be a continuation of the last line. The same goes for parentheses at the beginning of a line.

Source: http://blog.izs.me/post/2353458699/an-open-letter-to-javascr...

einaregilsson12• 15 years ago

Yes, the two cases where I actually think I could run into that are that and var x = i (function() {...})()

where it wil think i( is a function call.

sjs9• 15 years ago

The informal and single easy rule is to prefix lines that begin with punctuation with a semi. In practice only [ and ( crop up, almost nobody begins lines with a prefix increment or decrement. If you use += 1 and -= 1 instead you sidestep that case.

felipemnoa2• 15 years ago

Or, you could just add a semicolon. KISS at work.

hippich2• 15 years ago

my biggest concerns - why people want to _not_ use semicolons? Does it improve load speed may be? or make code more readable or help with something else?

beej71• 15 years ago

You point is doubly valid when you consider that the code might be run through Closure or Uglify, and all the truly extraneous semicolons will be removed. At that point, load speed is maximized, and the code is unreadable, semicolons or otherwise.

Since JS source "feels" more C-like than Python-like to me, I think the semicolons are a good idea.

einaregilsson12• 15 years ago

Well, I think it's more readable without semicolons. Less linenoise. And after reading about exactly how it works I'd rather omit them where I can. The cases where it behaves differently than expected are almost all cases where I think "I would never do that anyway"

carussell• 15 years ago

Why are writers afraid of not capitalizing the first word of sentences in English but don't care in Korean?

Won't you consider it? Less line noise, you know?

bluesnowmonkey5• 15 years ago

Readability. Python, Ruby, and CoffeeScript are more readable for their parsimonious approach to punctuation, aren't they? We like those languages, right?

burgerbrain3• 15 years ago

For definitions of "we" that exclude "me" perhaps.

hippich2• 15 years ago

I am not in your "we".

Also, JS was not designed from start as semicolon-less language. If you prefer semicolon-less JS - use Coffee Script. Otherwise it is very hard to debug such code for someone who do not expect semicolon-less JS code.

vlisivka2• 15 years ago

No, WE are avoiding Python, Ruby and CoffeScript.

If you want good example, say "shell script" instead.

hullo• 15 years ago

Haven't seen mentioned yet that .html files and legacy tools have an extremely lax historical attitude towards whitespace. People of a certain age came to the web understanding that a space is the same as a tab is the same as a line feed, as far as browsers are concerned.

The (increasingly common) practice on minifying is just one offspring of that history, which is, to the main point, not shared with Python.

jpr• 15 years ago

That's a stupid question to ask. More appropriate would be: who on earth thinks that omitting semi-colons makes anything better?

bluesnowmonkey5• 15 years ago

Yukihiro Matsumoto and Guido van Rossum come to mind.

daeken• 15 years ago

It's pretty obvious from the context that the OP was referring to omitting semicolons in Javascript, not in other languages.

chc• 15 years ago

Also apparently Brendan Eich, since he included the feature in the language, continues to speak of it without shame and has used it on his blog as an example of what he'd like to see code look like (with the comment that "JSLint can suck it").

sjs9• 15 years ago

I do. And it works both ways:

"That's a stupid question to ask. More appropriate would be: who on earth thinks that omitting semi-colons makes anything worse?"

vlisivka2• 15 years ago

I have habit to place something at the end of sentence _._ I learned that in school _._

hsmyers• 15 years ago

If memory serves, IBM's PL1 used to insert missing punctuation that it (the compiler) felt was missing. This wasn't particularly well thought out and often caused problems that were very difficult to debug. I used to think of it as 'doing me a favor that I hadn't asked for' and grew to hate both the feature and the language (the language for other reasons). In the years since then I've tried to be consistent in avoiding any such feature. I find it much easier to go ahead and use what ever the language needs. If I use semi-colons, then I don't have to guess there after...

russell• 15 years ago

In several years of PL/I programming, the compiler correctly inserted a semi-colon exactly once and then aborted the compile. I remember because it was such a surprise.

ethagnawl• 15 years ago

I got into the habit of using ;s to avoid having "my feelings hurt" by JSLint:

    Problem at line 1 character 10: Expected ';' and instead saw '(end)'.

adatta02• 15 years ago

Dropping semicolons also breaks a good deal of minifiers.

sjs9• 15 years ago

No, it really does not. Try it on any minifier that actually parses the JS and not some subset of the language.

cam-• 15 years ago

When compressing javascript down, missing a semi-colon can cause broken js, especially in older IE browsers. Trailing commas on js object literals would also freeze an entire page in IE. When that happened it would often take several days in jslint trying to work out where the broken js was from.

bluesnowmonkey5• 15 years ago

If that's the case, then the compression tool isn't parsing the Javascript correctly.

sjs9• 15 years ago

Watch out or all the nutjobs who uses Crockford's broken compressor will come out of the woodwork to defend it.

haberman• 15 years ago

Google's JavaScript style guide requires explicit semicolons; rationale: http://google-styleguide.googlecode.com/svn/trunk/javascript...

bluesnowmonkey5• 15 years ago

The examples being put forth in defense of requiring semicolons are really weak.

  // 1.
  MyClass.prototype.myMethod = function() {
    return 42;
  }  // No semicolon here.
  
  (function() {
    // Some initialization code wrapped in a function to create a scope for locals.
  })();

There are at least two potential solutions here: 1) put a semicolon after every function declaration, and 2) put a semicolon before every self-executing function. Both work fine. Either way, you have to remember to put a semicolon somewhere, right? No difference in cognitive load. And if you say that #1 is easier to remember because it's more C-like, you've just blown your cover. You don't actually write C at your day job, do you? Because otherwise you'd realize that C does not require semicolons after functions.

  [normalVersion, ffVersion][isIE]();

Same thing. Just put a semicolon before lines that start with arrays like this. Also this code is crap.

  -1 == resultOfOperation() || die();

OK hold up, who really writes this stuff? Is this what code looks like at Google? Forget semicolons for a second and let's work on basic code readability. Explain the line aloud. "If resultOfOperation returns negative one, then die." Now write it.

  if (resultOfOperation() == -1) die();

Sweet, now people can read our code without juggling operator precedence rules in their head. Minor side effect: the semicolon issue goes away.

  return
  { foo: bar }

Really? Why oh why would you write such a thing and expect it to return the object?

einaregilsson12• 15 years ago

Exactly! The semicolon prefix can be put even more simply: Prefix any line that starts with punctuation with a ;

There, you've just fixed all the cases that are likely to go wrong.

ScottBurson• 15 years ago

In general, DWIM (Do What I Mean) is evil. We're better off being forced to say exactly what we mean than having the machine try to figure it out for us. This lesson has been learned repeatedly over the years by programming language designers -- though clearly, alas, not by everyone.

sjs9• 15 years ago

Reason #1: Every time it comes up everyone who uses semicolons but doesn't really know why pipes up with their misguided and misinformed views on why dragons will eat your heart if you leave them out. Just look at the comments here.

notSorella5• 15 years ago

My feelings exactly :3

JohnLBevan• 15 years ago

You should always endeavour to make your code easy to read. Since most people aren't aware semi colons are optional, omitting them can cause unexpected behaviour in certain cases, and having them there does no harm, it's surely best to stick to the standards (i.e. using semi colons). The only time to debate whether to omit them is when there's a good reason to leave them out. Also, I suspect (untested theory) that it puts more strain on the parser, though makes negligible difference to the download speed, so will be a hit on performance.

Jach• 15 years ago

This is probably furthest down on my list of worries when writing JS... Sometimes I use semicolons, sometimes I don't (I try to be consistent in the same file), and when I'm in somebody else's house I follow their style. The examples given for why I should always use semicolons (e.g. the return + value on different line) are things that just don't come up for me and usually look ugly enough I'd avoid them anyway. (Also they're fairly simple to discover if you're actually testing your code.) The last time I did a return and value on the next line was in Java...

benbeltran• 15 years ago

All this discussion just makes me wonder: Why are some other programmers afraid of using them? It's just a semicolon.

Why are programmers afraid of not using semicolons in JavaScript?

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