A Declarative-Friendly API for Web Document Manipulation

The Document Object Model DOM is the document manipulation API provided to the JavaScript developer by the browser. It allows the programmer to update the currently displayed Web page from a client side script. For this, DOM primitives can create, remove or modify element nodes in the internal tree representation of the document. Interactive documents can be created by attaching event handlers and other auxiliary data to these nodes. The principle is interesting and powerful, and no modern Web development could be possible without it. But the implementation is not satisfactory when seeking predictability and reliability, such as expected with declarative languages or static type systems. Primitives are too generic, and when called in abnormal conditions can either throw exceptions or perform implicit imperative actions. In particular, DOM primitives can conditionally and implicitly move nodes in the document, in a way very difficult to be statically prevented or even detected. In this article, we introduce c DOM, an alternative document model that performs implicit deep copies instead of moves. By not moving their children implicitly, it preserves the structure of nodes after their creation and between explicit mutations. Side data embedded in the document are also duplicated in a sensible way so that the copies are completely similar in structure to the originals. It thus provides a more usual semantics, over which existing declarative abstractions and type systems can be used in a sound way.