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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.

Fri 23 Jun

ecoop-2017-papers
13:40 - 15:20: ECOOP Research Papers - Language and Library Design at Auditorium, Vertex Building
Chair(s): Sophia Drossopoulou
ecoop-2017-papers149821800000013:40 - 14:05
Talk
Daco HarkesDelft University of Technology, Eelco VisserDelft University of Technology
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ecoop-2017-papers149821950000014:05 - 14:30
Talk
Jack WilliamsUniversity of Edinburgh, J. Garrett MorrisUniversity of Edinburgh, UK, Philip WadlerUniversity of Edinburgh, UK, Jakub Zalewski
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ecoop-2017-papers149822100000014:30 - 14:55
Talk
Weixin ZhangUniversity of Hong Kong, Bruno C. d. S. OliveiraThe University of Hong Kong
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ecoop-2017-papers149822250000014:55 - 15:20
Talk
Tomas PetricekAlan Turing Institute
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