Why single var is good in javascript?

Question

Can anyone tell me why use one var declaration for multiple variables and declare each variable on a newline consider is a good programming behavior?

// bad
var items = getItems();
var goSportsTeam = true;
var dragonball = 'z';

// good
var items = getItems(),
    goSportsTeam = true,
    dragonball = 'z';

Answer 1

It is not considered 'good' or 'bad'. It's a matter of preference.

The guy who built the code quality tool JSLint, Douglas Crockford likes it.

One 'advantage' it might have is that it avoids the possibility of variable hoisting. In JavaScript all var declarations move to the top of their scope automatically.

Here is why Crockford thinks the second option is better:

In languages with block scope, it is usually recommended that variables be declared at the site of first use. But because JavaScript does not have block scope, it is wiser to declare all of a function's variables at the top of the function. It is recommended that a single var statement be used per function. This can be declined with the vars option.

Answer 2

It's a preference, I wouldn't say good or bad. Yes JSLint complains about it, I don't really like how it complains about for loop variables being inline as well. The reason that it was put in JSLint was to prevent possible hoisting confusions.

Also in some cases declaring all of your variables at the top will lead to a slightly smaller file. Consider the following:

var a = 10;
a++;
var b = 20;

After Google Closure being run over it

var a=10;a++;var b=20;

As opposed to this if we pull b's declaration to the top.

var a=10,b;a++;b=20;