ansaurus

Question

Answer 1

+4 A:

if ((typeof(oldins) != "undefined") && (oldins == ins))

etc 2010-07-13 13:39:24

+1 for being the right answer. Btw, no need for the parentheses around the `oldins` in the `typeof` check: `typeof` is an operator, not a function.

Tim Down 2010-07-13 14:17:56

Answer 2

+3 A:

Unset variables would evaluate to a value of 'undefined'. 'undefined' is a value type like null and NaN so it would be:

if ( typeof(oldins) == 'undefined' )

Edit: Fixed per comments. Leaving the answer since the comments are helpful, but there were more correct answers.

MacAnthony 2010-07-13 13:40:34

Well `undefined` is not exactly like `null` or `NaN` - it's just an identifier and it can be reassigned!

Pointy 2010-07-13 14:03:27

This will give you an error if `oldins` has never been declared. Use `typeof` instead.

Tim Down 2010-07-13 14:19:49

Who wouldn't declare their variables??? ;)Fair comments

MacAnthony 2010-07-13 14:43:14

@Pointy: Actually, `NaN` is also a variable as is `Infinity` - both can be reassigned. `null` is the only true keyword among these.

casablanca 2010-07-13 14:49:28

@casablanca wow really? Well after I typed in that comment I was going to try those but I got distracted, so thanks!!

Pointy 2010-07-13 18:49:36

Answer 3

+1 A:

if (oldins !== undefined && oldins === ins) {

}

bjg 2010-07-13 13:44:48

This will give you an error if `oldins` has never been declared. Use `typeof` instead.

Tim Down 2010-07-13 14:19:14

How to handle a not defined value in java script