Variable performance suggestion is wrong

[btipling]

https://github.com/jquery/learn.jquery.com/blob/master/page/performance/variable-definition.md

This is wrong, try it in jsperf:

http://jsperf.com/variable-definition

Variables on one line offer no benefit in Chrome and are slower on Firefox. Please remove this suggestion.

[ajpiano]

You are correct -- Both operations are coming up nearly five hundred million ops per second, so the real lesson here is not that one is faster than the other, it's that this doesn't belong in the Performance section at all. The fact that var can be comma-delimited is a language/code style issue.

[rmurphey]

This is content that came from @paulirish's talk at the 2009 jQuery conference, "Antipatterns for Performance and Compression." Needless to say, it's a bit outdated, but it does seem useful to point out that both styles will work. I remember there was a time when this was news to me :) It may also be useful to link to @cowboy's discussion of the merits of each style.

[paulirish]

it might be worth keeping as a style thing (though i wouldnt )
definitely shouldnt be kept as a perf thing.

[ithcy]

Interesting mini-survey regarding multiple vs. single var statements:

@douglascrockford in his Code Conventions: "It is preferred that each variable be given its own line and comment."
But then, @douglascrockford in the JSLint docs: "It is recommended that a single var statement be used per function."
@cowboy says "multiple var statements aren’t superfluous and they aren’t noobish. They reduce the effort it takes to maintain code."
@paulirish you've obviously called multiple statements "old 'n busted" and single statements "the new hotness" :) but I think this was more in regards to compressibility before smart minifiers were widespread?
@jquery's own style guide just calls multiple var statements "Bad" and single "Good" with no explanation.

So it appears the jury is still out to some extent, but does it really come down to personal style, or does anyone have a technically sound reason to recommend single var statements?

[ithcy]

@rmurphey useful to point out that both styles will work in a "learn javascript" guide perhaps, but in a "learn jQuery" guide?

[paulirish]

it was my 2009 perspective. the debugability of multiple vars greatly
outweighs everything else ever.

jury is in, on this one.

[btipling]

Just as a matter of style, I generally have one variable declaration line at the top of every function and assign separately later. This may seem strange, but I value not having to hunt or be misled about where var declarations are happening or in what scope, especially in the case of nested functions, and I find declaring and assigning values to variables all on the same line as hurting readability.

function foobar() {
  var width, height, x, y, foo;
  width = 200;
  height = 300;
  //do something
  x = someFunction();
 // etc.
}

This is too noisy for me:

function foobar() {
   var width = 200,
   height = 300,
   x = someFunction();
  // etc.
}

Just linting and style. Keeping functions small however really makes it mostly a non-issue and I strive for that.

Has nothing to do with performance though.

[paulirish]

seems good

[rmurphey]

I have no objections to removing this article. Probably worth reviewing the other perf content from the good old days of 2009 :)

[paulirish]

i basically kicked off a lot of microoptimization activity. i seek
forgiveness for my sins.

On Fri, Feb 22, 2013 at 7:08 PM, Rebecca Murphey
notifications@github.comwrote:

I have no objections to removing this article. Probably worth reviewing
the other perf content from the good old days of 2009 :)

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/256#issuecomment-13984029.

[mikesherov]

Hate to jump in late here with an informal poll, but regardless of onevar or not, do all the declarations belong at the top? I'm not arguing for or against onevar, but with onevar the declarations all happen at the top regardless of where assignment happens. If you're advocating for multiple vars, do you still feel stylistically that all declarations belong at the top?

P.S. @paulirish, I forgive you.

[btipling]

If you group your variable declarations at the top, preferably all on one line, you'll avoid problems such as accidentally attempting to refer to a variable one scope up without realizing you also declared a variable with the same name at the bottom of your existing scope. Disaster, and staring into the abyss for an unreasonable amount of time avoided. It's just easier to always have an easy way to scan variable declarations instead of peppering your code with them all over the place. I mentioned small functions, those are always important. If you look at the horrible code[1] of a project like flot, an actually cool canvas based charting tool, you can see playing the "what variable is this?" game in a huge function that contains other huge functions, this can be a very frustrating experience.

[1] https://github.com/flot/flot/blob/master/jquery.flot.js

[cowboy]

Oof. https://github.com/flot/flot/blob/master/jquery.flot.js#L151