Browsing
forums, development articles and other resource sites raised an interesting yet recurring question: "How do I test for Document Object Model (DOM) employed by a browser?". Strangely enough I was asking same question when starting out in Javascript. However, after enough time has passed, with same thing done more than once, I started to realise that this is a question that begs answering for once and for all.
A Typical Test
Testing for DOM in itself is easy enough. A recommended approach is testing for support of a DOM, and not for a browser version. The following describes Boolean variables that indicates compliance to DOM methods and parameters that you are targeting:
isIE4 = document.all? true : false; isIE6 = document.getElementById && document.all ? true : false;
isNS4 = document.layers? true : false;
isNS6 = document.getElementById && !document.all ? true : false;
The above items return a set of true or false values for any browser. This method still requires that you access objects described by DOM through that DOM's methods. In long run amount of work you have to do remains more or less same.
Javasript is an Object Orientated language
Everyone who is familiar with Javascript knows that language supports Object Orientation (OO). Passing objects around in variables is nothing new, so why do people persist in performing lengthy tests for DOM each time we need to access an object?
The item which describes document's referencing structure is nothing more that an object itself. This means that you only need to perform test once, and then proceed to use an arbitrary object that describes DOM object throughout remainder of your script. However, since this approach would require that you define a variable for each and every object you will be referencing, we need an approach which is more robust.
A Compromise
Typically you access objects though DOM for one of two reasons: Get a value, or Set a value. Previous approaches require that you access object through DOM methods each and every time you need to perform some action on object. The same holds true for every other object accessed by your script. What we need is a method that will:
- Access correct DOM using relevant methods
- Return object of interest
- Not waste time and patience
A practical approach used by myself is described in a function that returns your object without any hassles.
function getDOMObject (documentID){
