if(something == null) {}

because you will get an error saying that “something” is undefined.

you still have to do:

if(typeof something == ‘undefine’) {}

If you read plenty of books on the subject of JavaScript, all the authors never use should / should not, they simply explain the language, and leave it to the programmer to make his choice on syntax.

Remember JS is not like C where the coder has no choice but to organize his code religiously.

JS – It’s a do what the fuck you like language. That is, if you can even call it a language at all.

Describing two slightly different scenarios; If the value is unknown and you only declare the variable and don’t instantiate it in the var statement then an error will be thrown.

This throws an error (unless local4 and local5 have already been instantiated elsewhere within the global space):

 var local1 = 'local1',
        local2 = 'local2',
        local3;
        local4,
        local5;

As opposed to the following code which doesn’t fail, but has globals.

 var local1 = 'local1',
        local2 = 'local2',
        local3 = ‘local3’;
        local4 = ‘local3’,
        local5 = ‘local3’;

Here’s the fiddle http://jsfiddle.net/VXdQv/3/

Sorry I missed your point to begin with : )

No, you can it see for yourself here: http://jsfiddle.net/VXdQv/1/. Omitting var simply creates an implicit global variable.

Something along the lines of:

var 
   anonname
,  funct
,  functions
,  global
,  implied
,  inblock
,  indent
,  jsonmode
,  wsh = { /* ... */ }
,  functionicity = [
	'closure', 'exception', 'global', 'label',
	'outer', 'unused', 'var'
   ];

@Anton, if you popped in a semi-colon half way along, wouldn’t the interpreter would throw an error rather than cause the consecutive declarations to be global.

/* From JSHint/JSLint source code */
 
var anonname,
 
    /* 300 lines later we are still declaring variables */
 
    funct,          // The current function
 
    functionicity = [
        'closure', 'exception', 'global', 'label',
        'outer', 'unused', 'var'
    ],
 
    functions,      // All of the functions
 
    global,         // The global scope
    implied,        // Implied globals
    inblock,
    indent,
    jsonmode,
 
    /* ... */
 
    wsh = { /* ... */ };

I have seen numerous times when a person—who is new to the code base—comes in and accidentally ends a line with a semicolon instead of a comma making all consecutive declarations implicitly global. Oops.

The differences could be considered “semantic”. But there are bug and performance considerations for each evaluation type.

@Rick Waldron: +1 to the single-vs-double quotes too. Too much time is wasted tracking down JS issues caused by closing js expressions with the wrong quote — or inside DOM object events (onclick=”doThisWith(“that”);”). Our code review policy includes single quotes for JS, double for HTML attributes, always.

Thanks for the post and the excellent comments that have resulted.

var d = new Date.getTime(); /*Fails*/

And just for personal preference I also only use 1 var at the top but formatted using tabs, so it appears like a declaration block (I use jslint alot):

{
	var
		one   = 1,
		three = 3,
		nine  = 9;
 
	return one + three + nine;
}

Btw, I like your background. It gives a subtle illusion of distance 🙂