Lecture notes - April 3

• Objects
• var arthur = new Object();
arthur.quest = "Holy Grail";
arther.favoriteColor = "red";
• an abstract container for many kinds of data
• an object is actually a "reference" or pointer to something; not the thing itsef.
• theKing = arthur; doesn't copy the object - just gives it a new name.
  
  
• Example
  
  
• You can have objects within objects within objects ...
• arthur.holyHandGrenade = new Object();
arthur.holyHandGrenade.count = 5;
arther.holyHandGrenade.goes = "boom";
• tree structure
• parent is object above ; children are objects below; siblings are objects nearby in the tree
• The point of all this is "managing complexity" by hiding some parts within other parts.
  
  
• Each browser window has a built-in heirarchy like this one, full of data and methods.
• A "method" is a part of an object that does something; they're always follwed by parens.
  
  
• Mozilla has a DOM inspector Tool that can look at all these built-in object trees.
• They get complicated - and are somewhat different from browser to browser.
• But you can use them to do some pretty cool stuff.
• Since an object is a "pointer", they can even point to themselves, giving what appear to be circular structures.  (See document.defaultView.... in DOM tool.)
  
  
• the "window" object is the parent of the whole DOM tree. 
  
• all objects defined in javascript within a window are children of window
• but since it's so common, that it's name is implied
• even "arthur" is a part of this object; see the DOM tool.
  
  
• one important object : document (actually window.document)
  
• document.write(...) we've already seen
• document.width
• document.height
• document.bgColor
• document.fgColor
• document.lastModified
• Put these together with if(){...} to make a page that is different colors for different widths!
  
  
• other object methods mentioned in the text
• window.location   (the URL address)
• window.location = ...  (jump to a new page)
• window.open("newFile.html", "name", width=300,height=400)   - a pop-up !
  
  
• JavaScript has some built-in objects, like Math
• x = Math.PI
• y = Math.random()
• z = Math.round(x)
•    - quick quiz : why does random have the () after it, but Math.PI doesn't ?
  
  
• explore browser objects in class with DOM tool