The goal of this diatribe appears to be to justify CoffeeScript's design, but to me it counts against it. To be fair, I have never thought CoffeeScript was worth using, but here's the crux:
The pitch: "CoffeeScript is a better syntax for writing JavaScript."
The reality: "CoffeeScript does not behave like JavaScript in subtle, non-syntactical ways."
It is often suggested that people use CoffeeScript instead of JavaScript. But this understanding of CoffeeScript is inaccurate. CoffeeScript has different semantics from JavaScript, and the obvious expansion of CoffeeScript back into JavaScript is a wrong expansion. A knowledgeable JavaScript developer will make mistakes when making simple changes to CoffeeScript code that they did not write. They will have difficulty fixing bugs in CoffeeScript code.
If you like, you can be a CoffeeScript shop. Find senior developers who use CoffeeScript and teach junior developers to use it. Code will be a little easier to write, and, like nerf guns and foosball, you might seem like a superficially cool place to work. Like any new technique, you'll be out on your own. You'll run into bugs, you'll deal with toolchain support, you'll find optimization issues.
There are reasons to translate other languages into JavaScript. Macros, static typing, execution in other contexts. CoffeeScript gives you ruby-like syntax... To me, that just doesn't seem worth it.
CoffeeScript has different semantics from JavaScript, and the obvious expansion of CoffeeScript back into JavaScript is a wrong expansion
Nothing in the post supports this assertion. You may have your own reasons for feeling this way, but the difference between JavaScript and CoffeeScript with respect to the "var" keyword is neither subtle nor obvious, given that CoffeeScript does not have a var keyword.
The only possible source of literal misinterpretation would be to look at a CoffeeScript file and think that every variable that wan't a parameter was a global variable. This is extremely unlikely in practice.
I read you as being biased against using it. FIne with me, Chief, go your way in peace. But don't try to twist my example into support for a decision you have already made.
the difference between JavaScript and CoffeeScript with respect to the "var" keyword is neither subtle nor obvious, given that CoffeeScript does not have a var keyword.
Great, then every variable in CoffeeScript must be global, because that's the semantics of a non-parameter not be declared a "var" in JavaScript. Except that this is not an accurate translation, as the entire post goes on to explain scoping in CoffeeScript.
The only possible source of literal misinterpretation would be to look at a CoffeeScript file and think that every variable that wan't a parameter was a global variable. This is extremely unlikely in practice.
Screwing up scoping is an extremely common JavaScript mistake. If you showed me JavaScript-like code and told me there was a bug, the first thing I would point out is that you declared everything globally. Oh, that isn't the case in CoffeeScript? Huh, I guess you're on your own then, because I didn't learn your goofy alternative JavaScript syntax. Maybe you think the junior kid who has a bug in his code is going to properly explain the subtlety of CoffeeScript scoping.
FIne with me, Chief, go your way in peace. But don't try to twist my example into support for a decision you have already made.
It's offensive of you to dismiss my criticism in this forum. I am not prejudiced against new things, and while CoffeeScript doesn't seem like a worthwhile idea to me, it's community is far more offensive. CoffeeScript's demagoguery of JavaScript might impress some folks, but outside ruby-like syntax, CoffeeScript doesn't solve any fundamental issues.
So, "go your way in peace", and leave me to my thoughts, please.
As every debate ought to say, we're each entitled to our own opinions, but not our own facts. My opinion--which I believe I have demonstrated to be a fact--is that it is possible to write sane CoffeeScript that is lexically scoped and not subject to misinterpretation.
It is a fact that it is possible to write CoffeeScript code that requires careful examination of the file to understand what it does, code which can also change if you alter something somewhere else in the file.
My opinion--which I also believe I have demonstrated to be a fact--is that it is possible to write sane JavaScript that is lexically scoped and not subject to misinterpretation.
It is clearly possible to write JavaScript code that requires careful examination of the file to understand what it does, acode which can also change if you alter something somewhere else in the file.
I have zero quibble with you or anyone else feeling CoffeeScript doesn't solve a problem for them. I have zero quibble with you or anyone else saying "Notwithstanding the fact that CoffeeScript is a lexically scoped language, my opinion is that I hate it."
My only quibble--and it is minor--is that it is not possible to say that CoffeeScript function-local variables don't work like JavaScript function-local variables and that you can confuse the two, since without the var keyword nobody can look at a CoffeeScript file and think they are looking at function-local variables.
We both agree on the fact that a file with variables that are not parameters in CoffeeScript has different semantics from a file with variables that are neither parameters nor function-local in JavaScript.
If your opinion is that this is a fatal flaw, well, who am I to argue with the fact that this is your opinion? I have a different opinion, and we are both entitled to same provided neither of us claim it to be a fact.
My assertion is that CoffeeScript is not an alternative syntax for JavaScript because of differences in scoping. My opinion is that this is not a good design choice because it increases the separation from the original language, requiring that someone who already knows JavaScript additionally learn CoffeeScript.
You can take the rest of my original comment as a rehashing of my evaluation of CoffeeScript, since I only see it when it appers on Hacker News.
In practice, the scoping difference that you run into 99% of the time is that implicit var keywords are in front of variables that haven't been seen in the current scope, and you have to assign globals to your top level scope (window in the browser). How long did it take me to bridge that separation from the original language? Oh, about a minute.
I've made a one-time investment of a minuscule amount of time and have been raking in the saved time and effort from not having to type var statements or track down lack-of-var bugs.
Have you tried it? I had the same opinion for a while, but after I wrote some code, I found the translated code easy to understand - and the language itself helpful and consistent.
This post does not attempt to compare CoffeeScript to INTERCAL or JavaScript as an overall design exercise. It simply points out an error that some people have made in characterizing CoffeeScript as lacking lexical scope.
It does point out that it has function-level lexical scope and that it has a construct for creating block scope which is almost identical to "let" as found in Scheme.
You can decide for yourself whether this is an advance on JavaScript or a retreat to the 1970s. If I had to defend the entire language every time I discussed CoffeeScript, mys posts would contain even more verbiage and repetition than they already do.
>the difference between JavaScript and CoffeeScript with respect to the "var" keyword is neither subtle nor obvious, given that CoffeeScript does not have a var keyword
The thing that is subtle and nonobvious as a javascript programmer is the way CoffeeScript variables are scoped. They are not scoped like "var" variables in javascript. They are not scoped like "non-var" variables in javascript either. They have their own kind of scope that is unique to CoffeeScript.
Now you can argue that the way javascript scopes variables is wrong, and I'd agree with you. You can argue that the CoffeeScript way is better, and that's fine. But it makes it a different language from JavaScript, and it has all the baggage that goes along with that. You can't just treat CoffeeScript as "javascript with a nicer syntax"; you need to approach it the same way you'd approach learning any new language.
The thing I used to hate about smalltalk was having to define the temporary vars at the top of the method/block. Now it just seems like a great idea which clarifies any sort of ambiguity like this.
The implied "only" in that statement seems preposterous to me. For one thing, it's both an over- and understatement of CoffeeScript's featureset, and for another, it's sort of like saying "The printing press just let people print books faster ∗yawn∗."
(Well, OK, so CoffeeScript isn't quite the leap that the printing press was, but you get the point.)
Dumb question: why would I use CoffeeScript over something like PyJS (pyjs.org) or even (shudder) GWT?
I've worked on enough projects that I've come to view syntax as a cost and not a feature. It can sometimes be worth paying that cost if it gets you lots of features - but all the features you list already exist in Python, and presumably can be translated just fine by PyJS. Why an entirely new language syntax instead of something that you're likely using on the server as well? Or is CoffeeScript basically Javascript with Ruby syntax?
>but all the features you list already exist in Python
Not all:
- string interpolation is way more flexible in CS
- splats are sort of partially covered by several python features, but not nearly so elegantly
- the existential operator is not found in Python at all; you have to test against None instead. Also, Python does not have anything like the "soak" feature that the existential operator does.
- No really, readable regex. Python still doesn't even have a literal notation for regexes, but CoffeeScript allows multiline literals with comments, ignored whitespace, and interpolation.
Also, I don't think that lowboy mentioned multiline lambdas, but yeah, multiline lambdas.
I once thought as you do that syntax is secondary and that what really matters is functionality. That was before I started using CoffeeScript. The thing is, syntax isn't important for the sake of making it a pleasure to write. It's important for making it a pleasure to read. And odd scoping scenarios notwithstanding, CoffeeScript is exceptional in that regard.
Here's an example. String interpolation in CoffeeScript is incredibly simple:
console.log "Hello #{name}, how are you doing?"
translates to
console.log "Hello"+name+", how are you doing?"
That's all. Typing it out, CoffeeScript saves you one keystroke. But there is a subtle boon to readability in the interpolation syntax. The first line says "We're placing the result of an expression here". The second line says "We're ending the string, concatenating the result of an expression, and then we're going to concatenate another string to that." The canonization of the idiom into syntax lets your brain relax and stop trying to translate.
CS is more than just syntactic sugar, but speaking in terms of syntax it has a more minimal mindset like Python or Ruby.
The difference between source and compiled code is much much closer. CS has been designed as a pure abstraction of JS, whereas those other projects take full-fledged languages with all of their idoms and features and make JS out of it. I agree that new syntax is a cost, and in general that we should fear abstractions. PyJS seems like it's more of a web framework (as is GWT) rather than a pure language compiler.
Python is a beautiful language, but just code in JS if you're working on the front end and are wary of CS. I'm a capable JS developer and it took me almost no time to get started with CS. Sure, you hit snags here and there with oddball situations and sometimes you have to check the output, but the benefits definitely outweigh the learning costs.
The sad thing is that it actually does a lot more than that, but the docs are gloss over or omit a lot of the subtle headache relief CoffeeScript provides. For example, in addition to making regular expressions readable by allowing a block syntax, it also allows regex interpolation, so this code:
blah = "crayfish"
pat = ///#{blah}///
is equivalent to:
pat = /crayfish/
This is in the docs, but if you blinked, you'd miss it.
lowboy's summary is good. If you avoid JavaScript but are familiar with it, you should give CoffeeScript a try. I've always thought JavaScript got a bad rap from being misused, but I have never been fond of its syntax.
I used to use Python when I needed a more powerful calculator, or when when I needed a script to automate something tedious. Now I go to CoffeeScript for both of those use cases.
The pitch: "CoffeeScript is a better syntax for writing JavaScript."
The reality: "CoffeeScript does not behave like JavaScript in subtle, non-syntactical ways."
It is often suggested that people use CoffeeScript instead of JavaScript. But this understanding of CoffeeScript is inaccurate. CoffeeScript has different semantics from JavaScript, and the obvious expansion of CoffeeScript back into JavaScript is a wrong expansion. A knowledgeable JavaScript developer will make mistakes when making simple changes to CoffeeScript code that they did not write. They will have difficulty fixing bugs in CoffeeScript code.
If you like, you can be a CoffeeScript shop. Find senior developers who use CoffeeScript and teach junior developers to use it. Code will be a little easier to write, and, like nerf guns and foosball, you might seem like a superficially cool place to work. Like any new technique, you'll be out on your own. You'll run into bugs, you'll deal with toolchain support, you'll find optimization issues.
There are reasons to translate other languages into JavaScript. Macros, static typing, execution in other contexts. CoffeeScript gives you ruby-like syntax... To me, that just doesn't seem worth it.