Capability Detection

• JavaScript uses Associative Arrays
• Every method fills a slot in an array
• ex. the ie4 all collection on the document

    document["all"] == document.all

• Any "unfilled" slots return null
• Use this to check for support:

    var supportAll = (document.all!=null)
    if (supportAll) {
      // Browser supports the all collection
    } else
    {
      // Do something else
    }