1. Cooperative multitasking. Really? In 2014? Hello?
2. Weakest of weak typing. undefined is not a function? Anyone?
3. Everyone can override everything.
4. Conventions, that's the only way you can build software in JS. Anyone know of a person who doesn't break conventions?
Having programmed in something like Erlang, which IMHO is the sanest technology available today for doing web, JS feels horrible.
1. It turns out the reactor pattern is a good way to build network servers that scale reasonably well with minimal developer effort. In my experience developers tend to avoid writing threaded code in synchronous languages, and threads don't show up very often in run-of-the-mill solutions. To be sure, JavaScript's lack of threads is a blemish, but oddly it forced the community to focus heavily on distributed architectures, and as a result most of the tooling encourages distributed systems, which is a win for some common use cases.
2. Type safety is a hotly debated topic and I don't think you can find resolution on this one. For some people, "weakest of weak typing" is a benefit.
3. Static vs. dynamic, see #2.
4. Do you mean that everything must be enforced by convention instead of static code analysis, compile-time checks and type safety? If so, I think you're making the same point three times.
Erlang is a beautiful language and may be the most correct in some sense, but doesn't look nearly as attractive to the kinds of teams I work on when you start to consider developer availability, library ecosystem, tooling, ISP support, documentation and community.
They're both good, in both cases.
2. Weak typing is a nice feature for prototyping, but for larger projects, a stronger type system is better at catching bugs. Many JavaScript programmers (myself included) are used to using separate systems to check types for them. My team uses the Closure Compiler, which, along with compiling the JS to a more optimized version, is also happy to check all your types and fails to build if your types don't line up.
3. Again, I believe this is something that you can make sure that the compiler catches. And, of course, anyone can write bad code (in any language); if you're overwriting stuff halfway across the codebase, then that's "bad code" and you should avoid doing that (and during the code review stage, you should be making sure that your coworkers don't do that either).
4. Like for any language, have guidelines for how you write code, and enforce some of your conventions with the compiler and with linting tools. It leads to a more consistent codebase.
Doing CPU-bound computation in your application server is an anti-pattern. IO-bound computation, however, is where Node excels.
The thing to realize is that pre-emptive multitasking is costly. It is convenient for the programmer (the programmer doesn't need to worry about blocking and locking up the rest of the program), but it comes at a cost. Lightweight "green" threads, or equivalently, Node's evented dispatch mechanism, are a much more efficient use of the CPU. For applications composed of short-lived computations (e.g., < 1ms), it doesn't make sense to interrupt them and context switch. It's more performant to let them complete and then switch. You just have to make sure you aren't doing any CPU-intensive computations in the app server—which you probably shouldn't be doing anyway.
The downside of Node's approach is callback hell. And that's why we have Go.
Yeah, preemptive multitasking may be costly. But as you say, when you have lots of users, most of their tasks are sleeping or waiting for timers. That's where preemptive multitasking excels. You can have millions of sleeping tasks and several (at times) doing real work. That's why Erlang is "scalable" and node.js is not. Especially if you need to have state in your workers and if you need them to live longer.
Saying that node's cooperative multitasking excels in IO-bound computation is a clear sign that you haven't tried Erlang.
I have another counter-point for this as a rails developer tinkering with golang recently. I think Go got this correct in many ways. Having light weight goroutines that can scale well; having good IO which does epoll/libuv style wait in the background transparently when you read/write. Easy to understand multiprocessing language in general. I have no idea why it's not taking off in web development though.
Wat?!
By the end of the 90's, people started the "10K project", aimed at adjusting Linux and Apache so that a hight-end machine could support 10k simultaneous Apache threads, all doing IO at the same time. And they were successfull.
That was more than 14 years ago.
Have you used Async.JS? In my experience, it has always solved my deep callback problems.
Not a good idea, but that's rarely a hindrance for both enterprisey and startup "human resources" management. Reminds me a bit of how we treated torchbearers and henchmen in D&D...
And lo and behold, they have decided that an anonymous class with only one method is equivalent to an anonymous function object, and given us syntactic sugar to invoke it without the class declaration boilerplate.
You're essentially doing the same as complaining that conditionals aren't a Smalltalk language feature.
Contrast with JavaScript, where functions are first-class, can be declared at top level, can be passed as arguments to and returned by other functions, can be called by dereferencing a variable, can be nested, can be partially applied, etc.
The minimal syntactic sugar for anonymous inner classes added in Java 8 doesn't even begin to approach the power of the function support in languages like JavaScript. Language-level support for this stuff matters.
Many uses of first-class functions is for reducing boilerplate to begin with.
Also to respond to your points...
1. This I see as the most valid argument, but not a deal-breaker (see Walmart, LinkedIn using Node without problems scaling).
2. Check out Flow by Facebook [2] or TypeScript.
3. Not true with require/modules.
4. It's incredibly easy to include a JSLint file in your repo and as a git hook.
[1] http://nerds.airbnb.com/isomorphic-javascript-future-web-app... [2] http://flowtype.org/
I find this sentiment odd. Obviously it's not ideal for many workloads, but for some things it's the sane option. I work with Tornado in python at work and cooperative multitasking is probably the thing I'm thankful for the most. The server is very IO bound, so it keeps logic seemingly synchronous but hasn't shown any throughput issues thus far.
2,3,4. TypeScript, Flow, PureScript add varying degrees of strictness, checking and purity (from low to high, in that order)
Erlang feels very complicated. I mainly build simple CRUD apps. Would I still benefit from using Erlang?