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JavaScript Object Hierarchy

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Introduction To Object Speak

JavaScript has broken down the components of a web page into objects. An object in simple computing terms can best be described as follows:

  • An object has properties: a colour is a property.
  • An object has methods: a method allows an object to be told to do something, for example, open up a window, or display a yes/no dialog box.
  • An object has events: it allows the object to tell the outside world that it has something to say about itself, should anybody be interested. For example a checkbox would "fire an event" were it to be checked or unchecked.

Notes:

  • objects can contain other objects. For example a color can be considered as an object, composed of Red Green and Blue properties.
  • Methods are usually used to do perform some action. Some methods "return" a value or object (as explained in the discussion of JavaScript variables).
  • Methods and events pass parameters. For example the window.open() method has parameters to specify what the window should look like (width, height ...).

There's a lot more to object oriented programming, but we'll skip the part where confusion usually sets in, it's easier to pick things up when they are needed.

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Object Hierarchy

The "object hierarchy" described here is extremely important. JavaScript is a programming language, the object hierarchy specifies all the objects JavaScript can manipulate. The objects described below are in a sense JavaScript's view of HTML pages.

  • Parent, Frames, Self, Top
  • Document
    • Location
    • History
    • Forms
      • Elements (text fields, textarea, checkbox, password, radio, select, button, submit, reset)
    • Links
    • Anchors

There are many more objects to peruse at your convenience. A good reference site is none other than Netscape's own reference manual .

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