Javascript module pattern with undefined specified

Question

I believe jQuery uses undefined in the module pattern to avoid it being redefined to an unexpected value. I thought about doing this but whenever I compare undefined I tend (always?) to use

typeof foo === 'undefined'

So is there any point doing this:

(function (win, doc, RG, undefined)
{
  // App goes here

})(window, document, typeof RGraph === 'object' ? RGraph : {});

Because then you'd be passing in the global value of undefined - which could be 2 if some, ummm, clever dick had reassigned it. — Richard
– Richard, Commented Dec 19, 2013 at 10:45
If you have a reliable undefined to compare to as per the method you show then you don't need to use typeof (unless you want to check a variable that might not have been declared), so that makes your code a bit simpler. If you plan to use typeof in all cases regardless then no, there's no point declaring undefined like that. Another way to reliably get the value undefined for comparison is to use void 0 - as in if(foo===void 0). — nnnnnn
– nnnnnn, Commented Dec 19, 2013 at 10:45
@nnnnnnnnnnnnnnnnnnnnn I just realised now that you've said that - it kinda makes my question moot. — Richard
– Richard, Commented Dec 19, 2013 at 10:49

Bergi · Accepted Answer · 2013-12-19 10:52:24Z

1

whenever I compare undefined I tend (always?) to use typeof foo === 'undefined'

Well if you don't use undefined in your module then there is no point in declaring it as a parameter to ensure its value.

However, there's a question mark after your "always", and you can hardly know who else might work with your code in the future, so it still might be advisable.

answered Dec 19, 2013 at 10:52

Bergi

671k162 gold badges1k silver badges1.5k bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Aadit M Shah · Accepted Answer · 2013-12-19 11:19:02Z

There are three ways to test whether a value is undefined:

Method 1: Use typeof:

if (typeof value === "undefined") {
    // do something
}

Method 2: Compare it with the variable undefined:

if (value === undefined) {
    // do something
}

Method 3: Compare it with void 0:

if (value === void 0) {
    // do something
}

Q: Which one should you use?

A: There are many factors to consider:

In terms of understandability typeof and undefined are the best.
In terms of minimum characters undefined is the best when minified.
In terms of performance (http://jsperf.com/type-of-undefined-vs-undefined):
1. Both undefined and void are at par in most browsers (notably Firefox and Chrome).
2. In Chrome typeof is slower than the other two but in Firefox it is the fastest.
Using typeof is the only way to test whether or not a variable exists.

Based on these factors I would say that undefined (method 2) is the best method. There's always the problem of undefined being overwritten. However if you're using the module pattern (which you should be doing in the browser) then you can get undefined for free:

(function ($, undefined) {
    // you can use `undefined` safely here
}(jQuery));

Hence if you're using the module pattern then I would suggest you use the second method. It is readable, understandable and concise. The only disadvantage is that you won't be able to test whether or not a variable exists. However you can always fall back to typeof for that.

Collectives™ on Stack Overflow

Javascript module pattern with undefined specified

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related