How to avoid javascript retrieving values from non-existing elements

Question

Update: clarified question (I hope) Hi.

I'm developing a plugin in Wordpress and I'm outputting elements according to user privileges A and B.

In case of A, I ouput element "Foo".
In case of B, I output element "Bar".

Up till now, I haven't checked if an element exists before I try to retrieve the value. This of course gives me a javascript error in some browsers (like IE7).

I've looked at using the typeof() function:

if(typeof(element) == 'undefined') {
    //do something...
}

I'm also using jQuery. So one solution could be using this:

if ($("#mydiv").length > 0){
    // do something here
}

Using the above methods, makes me having to check each element before trying to retrieve any values.

The "ideal" solution would be to get values based on user privileges. E.g:

if (userPriv == A) {
    //get values from element 'Foo'
}

This way I can check once, and do the data gathering. The only solutions I can think of are setting the value of a hidden input element or use cookies.

<input type="hidden" id="userPriv" value="A" />

The other solution would be adding a value to the cookie.

setcookie("userPriv", "A");

Unfortunately, this last option gives me a warning message saying that cookie must be set in header (before html output). I think it's because I'm doing this in Wordpress.

I'm looking for opinions on which method is "the best way" to accomplis this.

Answer 1

You can use object as associative array:

var map = new Object();
map[A.toString()] = new Foo();
map[B.toString()] = new Bar();

In that case is much simpler to check and you will avoid "spaghetti code".

Answer 2

Forgive me if I'm missing something, but checking for a DOM element in javascript is usually pretty easy.

var elementA = document.getElementById('id_of_a');
var elementB = document.getElementById('id_of_b');
if (elementA) {
    //...
} else if (elementB) {
    //...
}

The key is the if statement. getElementById will return nothing null if the element is not found, which will evaluate to false in the if statement.

---

Alternatively, if you don't really want to check for existence of individual DOM elements, can you send the users priv in a hidden input and act on that? That's a cookie free way of sending values clientside. Something like (edited to have jQuery code instead)

<input type="hidden" id="userPriv" value="A" />
...

var priv = $('#userPriv').val();
if (priv == 'A') {
    //...
}

I'd still recommend checking for individual elements over checking a hidden input. It seems cleaner to me, more along the unobtrusive lines