javascript - an array of arrays, counting indexes

Question

HI,

I am looking at this bit of code:

var length = 0;
for (recordId in publicationTableIndexes[sortColumnNumber]){
 length++;
}

And I am wondering if there is a way of getting the same result without the loop?

publicationTableIndexes is an array containing 5 arrays. If I try publicationTAbleIndexes[sortColumnNumber].length I get undefined.

Ideas?

Thanks, Ron.

Ok, as per the suggestions I did some testing and realised that the sub element is actually an object. The construcotor code:

function sortTableByCreatingIndex(table, sortingColumnNumber, sortOrder, superTable){
var length = 0;

//Length -1 due to the array doing an upwards comparison, if length not adjusted null object error.
length = table.length - 1;

for (recordId = 0; recordId <= length; recordId++){
    this[recordId] = recordId;
}

I actually haven't encountered the 'this' usage before and was quite intrigued by it. What I am interested in knowing how do I take it out and define it as an array. How does 'this' work because looking at the code its not obvious where it is getting its values from, a bit kind of 'like magic' it knows what object to reference.

Thanks, R.

Answer 1

Sounds like the data in the array is not what your expecting it to be. What i would do is get firebug, and put in the following just before your loop

console.debug(publicationTableIndexes);

That will show you the entire contents of the array, and you can see what is exactly in it.

Answer 2

The data stored in each entry in your publicationTableIndexes is probably being stored using an object which doesn't have a .length property.

SO5223 covers the 'best' way to determine the length of an object.