The WebKit Open Source Project

Major Objects in WebCore

Adam Barth
first draft, 2009-08-12

WebCore uses a number of objects to represent a web page in memory. This document describes the major objects and the relation between them. In some cases, the connection between these objects can be broken, resulting in null pointers. When traversing these pointers, code must be careful to consider the "detached" case and gracefully handle null pointers.

 +---------+
 | Chrome  |
 +----+----+
      |
  +---+---+     +----------+
  | Page  +---->| Settings |
  +---+---+     +----------+
      |
      +-------------------------- ... other Frame objects
      |
  +---+---+   +-------------+                 +-------------------+
  | Frame +---+ FrameLoader +                 | JSDOMWindowShell  |
  +---+---+   +-------------+                 +---------+---------+
     / \                                                |
    /   \      /\  Re-used after navigation   /\        |
.../....|...............................................|..........
  /     |      \/  Replaced after navigation  \/        |
 /      |                                               |
/<------|<-- Ptrs to Frame are null after navigation[1] |
|       |                                               |
| +-----+-----+         +-------------+                 |
| | DOMWindow |<--impl--+ JSDOMWindow |<------window----+
| +-----+-----+         +-------------+
|       |
|       |<-- Can be null for Documents created by XMLHttpRequest
|       |
| +-----+-----+         +-------------+
+-+ Document  |<--impl--+ JSDocument  |
  +-----+-----+         +-------------+
        |
        |<-- Can be null for DocumentType objects
        |
    +---+---+           +--------+
    | Node  |<---impl---| JSNode |
    +-------+           +--------+

[1] After navigating to a new page, the old DOMWindow and old Document point to a null Frame, and the Frame points to a new DOMWindow and a new Document.

If you have any comments on the above or other ideas about improving the clarity, scope, or presentation, please send mail to the WebKit mailing list.