JavaScript global variables & self-invoking anonymous functions

Question

So I've been reading through Javascript - The Good Parts and one thing that Crockford points out is the use weakness of global variables in Javascript, in such a way that if your product is expanded in some manner, and it relies on a 'global' variable it could be inadvertently set.

That's all good and fine and I understand the pros/cons of protecting variables, in other manners such as closures as well. However, I was doing some thinking, and wrapping code in a function like so:

(function () {
    var x = 'meh';
})();
(function () {
    alert(typeof x); // undefined
})();

gives it variable scope, which thereby prevents cross contamination of variables. I'm not sure if there's a blatant downside to this approach though and wondered if the community had any input, or if I'm just overthinking things and ignoring the main point.

Sean Vieira · Accepted Answer · 2010-10-28 17:58:24Z

7

That's a perfectly legal way of doing things -- the variables inside of your function (as long as they are prefaced by var) are local to the function. It's called the module pattern, and it's very well accepted.

edited Oct 28, 2010 at 17:58

answered Oct 28, 2010 at 17:22

Sean Vieira

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3 Comments

A Wizard Did It Over a year ago

Awesome. Appreciate the link. I wonder why this isn't really mentioned in his book (so far, it's possible it is later, but it'd make sense to have it in the part bashing global variables). At least I know I'm not being overly analytical for once.

Marcel Korpel Over a year ago

This is my nit-picking day, apparently, but those things are not called closures in a strict sense (in a general computer science sense, all JavaScript functions are closures): those self-invoking anonymous functions would only be closures if they are used outside of the scope in which they were defined (e.g., when attaching an anonymous function to an event listener within a function that exits before the listener is detached).

Sean Vieira Over a year ago

@Marcel -- thanks, I've updated it to use function rather than closure.

szanata · Accepted Answer · 2010-10-28 17:31:57Z

0

To create applications with javascript, you must attempt to keep variables in a local scope, and anything inside a namespace. It's a good pratice and prevent a serie of harm codes and unespected behaviors.

read this

it's a article talking about the vantages of doing that.

answered Oct 28, 2010 at 17:31

szanata

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Comments

AutoSponge · Accepted Answer · 2010-10-28 18:53:43Z

0

Making it a global function is not the answer. Why wouldn't you do this? This keeps x out of the global namespace.

(function () {
    var x = 'meh';
    alert(typeof x);  //string
})();

answered Oct 28, 2010 at 18:53

AutoSponge

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1 Comment

A Wizard Did It Over a year ago

The point in the example was to get undefined, therefore isolation from eachother.

Andy Grizzly · Accepted Answer · 2018-11-20 15:03:55Z

0

(function (global) {
    global.x = 'meh';
})(window);
(function () {
    alert(typeof x); // string
})();

answered Nov 20, 2018 at 15:03

Andy Grizzly

1

1 Comment

user12867493 Over a year ago

Please try to avoid code only answers and add some detail or explanation. Thanks

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