Thursday, January 13, 2011

Firefox and undefined array elements

So here's a Javascript question. Now I admit I'm not a Javascript expert so this ones got me a bit stumped.

In the following code snippet I'm trying to get a function to do something only when it is
first called. It can be called with a number of items (identified by an integer I), it
should call itself only the first time it is called with that arguement. I have an array (lsaCall)
with only the first item defined (and set to 0). If the array element is undefined (or 0) then the function
calls itsel on a timer.

var lsaCall = [0];
function loadSubscribedArticles(i,tag,Author){
 //alert("lsaCall "+lsaCall[i]);
 if ((lsaCall[i]==undefined) || (lsaCall[i] ==0)) {
  var int=self.setInterval("loadSubscribedArticles('"+i+"','"+tag+"','"+Author+"')",1000);

This works fine and dandy but doesn't work at all in firefox. It complains that lsaCall
is undefined (well I know that !)
Any ideas on how to get this working in firefox ? Is there a better way of doing it ?


  1. Hey Andy,

    I think Firefox is just having a problem with the 'undefined' check. I've rewritten the function to use stricter checking. The typeof operator returns the type of an object as a string, and all browsers are happy with its usage. I've also turned your == equality checker to ===. == and != use JavaScript type casting to check for truthys and falsies across types, but using === and !== enforces the type.

    Here's the updated code:

    I also moved your int declaration to the top of the function because that's what JavaScript does at runtime. By forcing yourself to declare all vars at the top of a function, you can avoid a lot of head scratching later on!

  2. I liked the content on this site. Would like to visit again.

    Direct Mail Advertising
    Direct Mail Letter

  3. JBN CREATORS is Ecommerce Website Development company in DELHI. We have more than 5 years of experience serving outsourcing web development services. Provide you service in affordable price at right time. Feel Free contact us 8802969543 , 9650829282 .
    Ecommerce Website Development