CODEWITHSUNDEEP
javascript
zer0c00l
zer0c00l

Reputation: 303

javascript typeof item === "undefined" never returns true

In the following code sample, typeof item === "undefined" never returns true. i am trying to get an attribute from XML, if the attribute is not there in the XML it returns "undefined", but i am not able to capture whether it has returned undefined or not, firebug shows "typeof item" as an "object"

var item;
var itemIDs = {};
if (items.status == 200)
{   
    var rows = items.responseXML.getElementsByTagName('z:row');
    for(i=0;i<rows.length;i++)
    { 
        //rows[i].attr(attribute);
        item = rows[i].getAttribute(attribute);
        if(typeof item === "undefined")
        {
            continue;

        }
        else
        {
            item = item.match(/[^\d+;#][\w\W]+/);
            itemIDs[item] = 1 ;
        }

    }
}
else
{
     alert('There was an error: ' + items.statusText);
}

return itemIDs;

Edit: I changed the condition to if(item == undefined), The code now works as expected now

Edit2: Double checked it, item variable was never null , it was "undefined"

Upvotes: 0

Views: 1543

Answers (6)

Salman Arshad
Salman Arshad

Reputation: 272096

typeof null is "object"... this is what getAttribute seems to return when the attribute is missing. See documentation of element.getAttribute, specifically the notes section. It is suggested that you can use hasAttribute.

Upvotes: 1

vol7ron
vol7ron

Reputation: 42099

getAttribute : return type object

you should compare return value to null

Upvotes: 0

RoccoC5
RoccoC5

Reputation: 4213

Some browser's implementation of getAttribute may return an empty string if the attribute doesn't exist. You could test for both null and "", or alternatively use hasAttribute.

if(rows[i].hasAttribute(attribute))
{
    // do stuff...
}

https://developer.mozilla.org/en/DOM/element.getAttribute

Upvotes: 2

denyo85
denyo85

Reputation: 79

try this:

if (!item)
{
    continue;
}
else
{
    item = item.match(/[^\d+;#][\w\W]+/);
    itemIDs[item] = 1 ;
}

this proofs if the item is null or undefined. is this true, it continues the loop.

Upvotes: 0

bhups
bhups

Reputation: 14885

getAttribute returns an object (valid object or a null object). So the check (typeof item === "undefined") is not correct. It should be (item === null).

Upvotes: 3

katspaugh
katspaugh

Reputation: 17899

It's because typeof null === 'object' (contrary to the common sense). You should check if getAttrbiute's return value equals null.

item = rows[i].getAttribute(attribute);
if (item == null) { /* ... */ }

Upvotes: 1

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