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diff --git a/comm/mailnews/jsaccount/readme.html b/comm/mailnews/jsaccount/readme.html new file mode 100644 index 0000000000..cb1b875dbe --- /dev/null +++ b/comm/mailnews/jsaccount/readme.html @@ -0,0 +1,67 @@ +<!DOCTYPE html> +<html> + <head> + <meta charset="utf-8" /> + <title>JsAccount Usage and Architecture</title> + </head> + <body> + <h1>Overview</h1> + <p> + JsAccount is a technology that allows message account types to be created + in Mozilla Mailnews code using JavaScript. Although this is primarily + targeted at allowing extensions to create new accounts, it might also be + useful as a bridge to convert existing account types from being C++ based + to JavaScript based. + </p> + <h2>Existing C++-based architecture of mailnews accounts</h2> + <p> + In mailnews code, an account type is a set of classes that allow + implementation of a messaging particular protocol. The account type is + given a short string identifier ("imap", "news", "pop3") and is then used + to create objects of the appropriate type by appending that string to the + end of a base XPCOM contractID. So, for example, to create an imap server, + you generate a contractID using a base ID, + "@mozilla.org/messenger/server;1?type=", then append "imap" to get: + </p> + <p>@mozilla.org/messenger/server;1?type=imap</p> + <p> + In the C++ code, there is a base object implementing shared functionality. + An account-specific class inherits that base functionality, then extends + it to represent the account-specific behavior that is needed. This same + basic concept is used to represent a whole series of classes that are + necessary to implement a specific mailnews account type. + </p> + <p> + For the server example, there is a base class named + nsMsgIncomingServer.cpp that implements that base interface + nsIMsgIncomingServer.idl. For imap, there is a specific class + nsImapIncomingServer.cpp that inherits from nsMsgIncomingServer.cpp, + overrides some of the methods in nsIMsgIncomingServer.idl, and also + implements an imap-specific interface nsIImapIncomingServer.idl. All of + this works fine using C++ inheritance and polymorphism. + </p> + <p> + Although JsAccount is intended mostly for mailnews accounts, the same + basic method of using a base class extended for specific types is also + used in other ways in mailnews code, including for addressbook types and + views. The technology may also be applied to those other object types as + well. + </p> + <h2>Role of JsAccount</h2> + <p> + The JavaScript class system works very differently than the C++ system, + and you cannot use normal language constructs to override a C++ class with + a JavaScript class. What JsAccount allows you to do is to create XPCOM + objects in JavaScript, and use those objects to override or extend the + methods from the C++ base class in a way that will function correctly + whether those objects are executed from within C++ code or JavaScript + code. This allows you to create a new account using JavaScript code, while + using the same base class functionality that is used by the core C++ + account types. Thus a new account type may be created in JavaScript-based + extension. The technology may also be used to create JavaScript versions + of existing account types in an incremental manner, slowly converting + methods from C++ to JavaScript. + </p> + <p><br /></p> + </body> +</html> |