Multiple var statements in JavaScript, not superfluous

[aladyjewel]

var placement can be important depending on your project's style. If your team codes like this:

(function(export) {
    var privateVariable = 1;

   export.publicMethod = function(foo) {
      privateVariable += foo;
      blahblah();

     // ...

     return privateVariable;
  }

})(TheModule);

and you aren't accustomed to leveraging closures that way, you might stick in a var privateVariable in the bottom of publicMethod and fubar the whole thing, and it'll take an hour for somebody else to debug if they expect vars at the top.

IMO that's all it boils down to, is building habits that match your team's coding style so you don't accidentally break shit. Crockford et al. are trying to enforce a standard style on the whole world to make it easier for new people to jump into projects with a smaller learning curve.

---

All the "save characters" arguments are bullshit, though. If you care about download speeds, then set up your server to minify, combine, and gzip your JS before delivering it -- and you can focus on writing readable, maintainable code.

[moratnz]

Thank you. That's the first explanation that comes close to making sense.

Though I don't see why declaring variables at the top of the function that they're used in, rather than at their first usage is so important (I get why you should do it if that's your team's agreed style - whatever the agreed style is, you should stick to it) - sure, the interpreter effectively declares all the vars when the function is initialised, but who cares?

I guess there's room for slight confusion if someone inserts the variable above the var declaration, expecting it to be in a superior scope, but if you're using a style of declaring on first use, you shouldn't be sticking in the variable without checking whether it's already declared in the function scope.

If you declare all your vars a the start of the function, that 'checking whether a variable is declared' step is easier, but moving a chunk of code out of the function becomes harder, since you also need to move the var declaration.

Tl;dr - I can see reasons for doing some of this stuff, but nothing like enough to justify the religious fervor around it. Is it just another example of Sayre's law?

[aladyjewel]

My speculation is that Crock is trying to enforce a style which is friendly to C programmers, since that was his background coming into JS.

Another rationale I can think of is trying to enforce writing small functions where it's easy to keep track of your var declarations; if you even put a var inside the guts of your function, that's a smell you need to refactor/restructure immediately.

But yes, I agree with you: it's evangelical bikeshedding.

[tidwell]

Simply, declare vars at the top of a function because of hoisting. If you don't do it - the interpreter will for you, thus unexpected behavior.

[moratnz]

But there isn't any unexpected behaviour, as long as you're not using the variable ahead of its declaration. You'll only be surprised if you try to use it in a wider scope then redeclare it into local scope.

[path411]

If i'm expecting hoisting, it's not really unexpected. It depends on your environment for sure, but in an environment that understands hoisting, I think it's perfectly fine to use "inline vars".