2026-07-21T19:24:50Z https://drops.dagstuhl.de/oai

oai:drops-oai.dagstuhl.de:7264 2024-03-06T10:39:46Z ddc:004 open_access

Mixed Messages: Measuring Conformance and Non-Interference in TypeScript Williams, Jack Morris, J. Garrett Wadler, Philip Zalewski, Jakub Gradual Typing TypeScript JavaScript Proxies TypeScript participates in the recent trend among programming languages to support gradual typing. The DefinitelyTyped Repository for TypeScript supplies type definitions for over 2000 popular JavaScript libraries. However, there is no guarantee that implementations conform to their corresponding declarations. We present a practical evaluation of gradual typing for TypeScript. We have developed a tool for use with TypeScript, based on the polymorphic blame calculus, for monitoring JavaScript libraries and TypeScript clients against the TypeScript definition. We apply our tool, TypeScript TPD, to those libraries in the DefinitelyTyped Repository which had adequate test code to use. Of the 122 libraries we checked, 62 had cases where either the library or its tests failed to conform to the declaration. Gradual typing should satisfy non-interference. Monitoring a program should never change its behaviour, except to raise a type error should a value not conform to its declared type. However, our experience also suggests serious technical concerns with the use of the JavaScript proxy mechanism for enforcing contracts. Of the 122 libraries we checked, 22 had cases where the library or its tests violated non-interference. Schloss Dagstuhl – Leibniz-Zentrum für Informatik Jack Williams and J. Garrett Morris and Philip Wadler and Jakub Zalewski 2017 Is Part Of LIPIcs, Volume 74, 31st European Conference on Object-Oriented Programming (ECOOP 2017) InProceedings Text doc-type:ResearchArticle publishedVersion application/pdf doi:10.4230/LIPIcs.ECOOP.2017.28 urn:nbn:de:0030-drops-72640 https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2017.28 eng https://creativecommons.org/licenses/by/3.0/legalcode