var ie = (navigator.appName == "Microsoft Internet Explorer");
// myStyleObj is used to refer the style object of elem1 in the HTML page
myStyleObj = ie ? document.all.elem1.style : document.elem1;
Now, anywhere in the code where you want to refer to the style object attribute, all you need to do is refer to myStyleObj.
myStyleObj.visibility = "visible";
instead of writing...
document.elem1.visibility = "visible"; // for Netscape Navigator and,
document.all.elem1.style.visibility = "visible"; // for Internet Explorer
This saves you from lots of browser compatibility issues, and it also helps you to write structured code. Also, it is a good idea to keep an array of style objects (of the HTML tags of our interest), in the beginning, and refer to them by using an appropriate index whenever required.