JavaScript object creation methods

Question

I've been searching around Stack Overflow, and the web in general, for a decent explanation of something I'm seeing in some legacy JavaScript. So far I haven't had much luck, so I've decided to take the extreme measure of actually posting a question. :-)

The code isn't super old, but it pre-dates my involvement in the project and (of course) the developer who originally created it left before I got here.

So here we go:

Normally when I'm looking @ code that creates JavaScript 'classes' I see something like:

var SomeClass = function() { ..stuff.. }

...other code...

var objSomeClass = new SomeClass();

Also familiar is the JavaScript literal:

var someLiteral = { ..stuff.. }

...other code...

var someResult = someLiteral.someFunction();

What I'm seeing in the legacy code appears to be a combination of the two styles, and I've never seen anyone do this before. So what we've got is:

var someLiteral = { ..stuff.. }

...other code...

var objSomeLiteral = new someLiteral();

Also, in the same code are declarations like this:

function doStuff() { ..stuff.. }

...other code...

var objDoStuff = new doStuff();

Again, I've never seen anyone write code quite like this before.

Is this semantically incorrect code, or is there some valid reason for doing it this way that I'm just not aware of? Which is always possible, I make no claims to JavaScript expertise at this point.

The code definitely works, but if it's not 'good' code then I'm going to want to re-write it. Cuz I'm just anal like that. :-)

Thanks!

Your first and last case are the same. The only difference is that in the first case you have an anonymous function and in the last one a named function. Also it would be nice if you could provide a reference where you have seen the third case, as this is indeed invalid JavaScript. — Felix Kling
– Felix Kling, Commented Jan 19, 2012 at 16:30
I'd love to post the original code, but I feel like I'd have to heavily sanitize it first. Yeah, I know - it's JavaScript and technically anyone who really wanted to could look at it. But I'd still rather not post it, as it's tied into our User Authentication process. — Bob FiveThousand
– Bob FiveThousand, Commented Jan 19, 2012 at 19:46
Ok, so Case 1 & Case 4 are functionally equivalent. I didn't know that. Although it seems kind of obvious now that I'm actually thinking about it. :-) — Bob FiveThousand
– Bob FiveThousand, Commented Jan 19, 2012 at 19:54

RedRiderX · Accepted Answer · 2012-01-19 16:38:54Z

2

new <Object> is a syntax error. That's simply not valid JavaScript. The operand of new has to be a function.

Also using functions as constructors like you showed in your "class" construct example is a very common practice.

edited Jan 19, 2012 at 16:38

RedRiderX

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answered Jan 19, 2012 at 15:54

Raynos

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1 Comment

Bob FiveThousand Over a year ago

That's exactly what I thought. It's always possible that the particular block of code where I ran across this, is never actually executed in practice. Which would explain why things appear to be 'working'. Anyway, thanks for the help.

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