The jQuery attribute function returns undefined if the value of the attribute is 0. The HTML code below returns undefined if you select "Foo", but 1 if you select "Bar"

<select id="foo" onChange="alert($('#foo').attr('selectedIndex'))">

<option value="Foo">Foo</option> <option value="Bar" selected>Bar</option>

</select>

This is because of the following line (in jQuery 1.2.3 line # 178)

return this.length && jQuery[ type "attr" ]( this[0], name ) undefined;

The problem here is that the return value of the attr call is 0, which is evaluated as false, and thus passes to the and returns undefined.

one possible way to fix this is:

if ( this.length ){

var ret = jQuery[ type "attr" ]( this[0], name );

return ret === 0 ? 0 : (ret undefined);

} else

return undefined;