Javascript catchup undefined

Question

I have build an array loader with javascript.

When I directly click last, I get undefined. I tryed to catch it up with something like this

var lastWord = (function() {

            return function() {
            var resultWord = wordArray[--count % wordArray.length];
                if (typeof resultWord == "undefined")
                { 
                return false;
                }
                else 
                {
                return wordArray[--count % wordArray.length];
                }
            }
        }

}());

But didn't worked, any suggestions?

Why is everyone having anonymous functions return anonymous functions these days. So crazy! — thatidiotguy, Dec 04 '12 at 20:49
@thatidiotguy http://www.adequatelygood.com/2010/3/JavaScript-Module-Pattern-In-Depth — Frank van Puffelen, Dec 04 '12 at 20:56
But I don't see that outer function adding any value here. There are no parameters to the function and no local variables that the returned function closes over. It's just syntactic noise with no benefit. — Scott Sauyet, Dec 04 '12 at 21:02
@ScottSauyet I agree. This seems like an overzealous professor going wild with power. — thatidiotguy, Dec 04 '12 at 21:08
This should help: http://stackoverflow.com/questions/4467539/javascript-modulo-not-behaving — Scott Sauyet, Dec 04 '12 at 21:10

score 0 · Answer 1 · answered Dec 04 '12 at 20:51

0

The reason it is undefined for the first time is because there is nothing in wordArray at negative indeces. There is no "last" word before you have hit update. Does that make sense? It works fine after you have hit update once.

answered Dec 04 '12 at 20:51

thatidiotguy

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yeah I know that, but I want to catch it up, so nothing happens if the value is undefined – Johnny000 Dec 04 '12 at 20:54
See this question: http://stackoverflow.com/questions/776950/javascript-undefined-undefined – thatidiotguy Dec 04 '12 at 20:55
as you can see above I alredy tried `if (typeof VARIABLE == "undefined")` – Johnny000 Dec 04 '12 at 20:59
@Johnny187 Why is not in the fiddle then? You can't post different code in different places. Make a new one with the current code, and I will gladly look at it again. – thatidiotguy Dec 04 '12 at 21:08

score 0 · Accepted Answer · answered Dec 04 '12 at 21:27

Try http://jsfiddle.net/ayQH2/2/

The problem is that the sign returned by the modulus operator is the sign of its first operand. So, for example

(-17) % 12 // == -5 , not 7

This will probably work, and does not include the extra function wrappers:

var nextWord = function() {
    // silly work-around for negative modulus issue
    var index = (++count % wordArray.length) + wordArray.length
    return wordArray[index % wordArray.length];
};
var lastWord = function() {
    // silly work-around for negative modulus issue
    var index = (--count % wordArray.length) + wordArray.length
    return wordArray[index % wordArray.length];
};

There are plenty of other ways to deal with this. Perhaps a better one would be to ensure that count never escapes the proper range, doing something like

count = (count == wordArray.length - 1) ? 0 : count++; // increment
count = (count == 0) ? wordArray.length - 1 : count--; // decrement

Javascript catchup undefined

2 Answers2