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Robust Trait Composition for JavaScript

Tom Van Cutsem
Mark S. Miller
Science of Computer Programming: Special Issue on Advances in Dynamic Languages (2012)


We introduce traits.js, a small, portable trait composition library for Javascript. Traits are a more robust alternative to multiple inheritance and enable object composition and reuse. traits.js is motivated by two goals: first, it is an experiment in using and extending Javascript's recently added meta-level object description format. By reusing this standard description format, traits.js can be made more interoperable with similar libraries, and even with built-in primitives. Second, traits.js makes it convenient to create "high-integrity" objects whose integrity cannot be violated by clients, an important property in the context of mash-ups composed from mutually suspicious scripts. We describe the design of traits.js and provide an operational semantics for TRAITS-JS, a minimal calculus that models the core functionality of the library.