Why I dislike chains of comma-separated variables.

variables.js

//==================
// VARIABLES: START.
//==================

var foo = 'foo',

/*
  Some lengthy explanation about `bar`
  and what it does, why we care, etc.
*/
bar = 'bar',

/*
  Some complex stuff here, so we need to
  have a function that does some logic.
*/
baz = (function() {
  'use strict';

  var x = 1;

  if (/* condition */) {
    x = 2;
  }
  else if (/* condition */) {
    x = 3;
  }
  else if (/* condition */) {
    x = 4;
  }

  return x;
})(),

// More variables...

uno = 1,
dos = 2;

//================
// VARIABLES: END.
//================

This is why I think comma separated variable declaration is bad. It gets hard to read.

I much prefer a var for each variable declaration, and letting a JS minifier handle the optimization.

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More reading…

https://speakerdeck.com/nathansmith/red-dirt-js?slide=98

https://speakerdeck.com/nathansmith/red-dirt-js?slide=99

What about

var foo, bar, baz, uno, dos;

foo = 'foo';
bar = 'bar';
....

That works. But, becomes sort of a maintenance headache — "scroll to the top of the page (or function scope) to make a new var — scroll back down to where I was, and resume typing.

I'm aware of how variable hoisting works, and I feel like if/once you are, it's not that big of a deal.

Plus, JS minifiers that optimize code will change all the var foo, bar, baz… into a chain like that, for you.

I say put that burden on automation, not humans.

:)

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For what it's worth, the Node.js code style guide specifies using one var per variable…

https://github.com/felixge/node-style-guide#declare-one-variable-per-var-statement