Section: New Results

Certified JavaScript Semantics

Participants : Martin Bodin, Alan Schmitt.

JavaScript is the most widely used web language for client-side applications. Whilst the development of JavaScript was initially just led by implementation, there is now increasing momentum behind the ECMA standardisation process. The time is ripe for a formal, mechanised specification of JavaScript, to clarify ambiguities in the ECMA standards, to serve as a trusted reference for high-level language compilation and JavaScript implementations, and to provide a platform for high-assurance proofs of language properties. We present JScert, a formalisation of the current ECMA standard in the Coq proof assistant, and JSref, a reference interpreter for JavaScript extracted from Coq to OCaml. We give a Coq proof that JSref is correct with respect to JScert and assess JSref using test262, the ECMA conformance test suite. Our methodology ensures that JScert is a comparatively accurate formulation of the English standard, which will only improve as time goes on. We have demonstrated that modern techniques of mechanised specification can handle the complexity of JavaScript [25] , [24] .