Question

I’ve been struggling for months with a JavaScript problem where I have an array with a few properties, and later some of these properties are checked to decide whether or not to show a message to the user.

Now this all goes well on most systems (especially more recent browsers) but not so much on some of my client’s IE7 computers.

Now I just found out that somewhere in my code I initialize a new Array like below, but never actually set the value for ‘done’

var qar=new Array('question_no','pos','done');
qar['question_no'] = 1234;
qar['pos'] = 1234; //dont mind these numbers

Later in some for loop I check:

//check if this question was already shown
if(qar['done'])
   continue; //stop here, don't show message
//set done to true, so that this question will not be shown again
qar['done'] = true;
window.alert('messaged!');

Again, what goes wrong is that sometimes (actually pretty often, but not always) the message is not shown at all in IE7.

Now for my question to you: I know that qar[‘done’] should be undefined right after initialization, which makes my code work fine (in Chrome etc), but could it be that somehow in IE7 this situation is handled differently? For example that qar[‘done’] is not undefined, but some random value and therefore is sometimes considered true accidentally? Or is that a stupid thing to think?

If this is not the problem, then I don’t know what is..

Thanks in advance!

Answer 1

By doing this:

var qar=new Array('question_no','pos','done');

You are just creating array with indexes.

qar[0] will be 'question_no'
qar[1] will be 'pos'
qar[2] will be 'done'

in this case, qas[‘done’] will always be undefined.

Thats why its causing problems. You should either use javascript object instead of using an array.

But you can do something like this:

if(typeof qar['done'] === 'undefined'){
   qar['done'] = true;
   alert('messaged!');
}