The following single line does the job.

    document.getElementById('warning').style.display = "block";

Let’s take a look at the $ function. The code is:

    function $() {
        var elements = new Array();

        for (var i = 0; i < arguments.length; i++) {
              var element = arguments[i];

              if (typeof element == 'string')
                   element = document.getElementById(element);

              if (arguments.length == 1)
                   return element;

              elements.push(element);
        }
        return elements;
    }

It can take any number of arguments that can be the string ID or a DOM object reference and returns an array of object references. It is perfect for getting references to multiple elements. But, all the code comes with it whether or not it is needed.

In most cases, however, all you needed is to get one object reference for a string ID. Using document.getElementById is much more direct.There may be cases where either an ID or object reference are passed; for example, a function that is called from several other functions some where the object reference already exists. Then the following two lines would be useful.

    if (typeof element == 'string')
          element = document.getElementById(element);

If these lines are needed frequently, then wrapping them in a function would be justified.

You might say the performance hit is less than a nano second, which is probably true. There are two extra objects created (a scope object and an array) as well as the overhead normally associated with a function call. All of which are normally not noticeable. However, inefficiencies like this accumulate especially if they are used in a loop. In highly dynamic interactive RIA sites, performance can become an issue and every little improvement will contribute to reaching acceptable results.

Have you come across similar issues? Or, do you feel that processor speed and cheap memory provide all the performance necessary? Let us know.

Read more from Lawrence O'Sullivan.