My Master’s Thesis on programming language and type system theory is published. The thesis explores several languages and approaches to statically typed Javascript-compiled languages. Find the thesis here.


JavaScript is a ubiquitous programming language with usage in web, mobile applications and server software. The status of the language as the de-facto programming language of the web has made the language ecosystem advanced with a great number of userspace libraries and major companies working on efficient runtime systems. The core language, however, has numerous known difficulties caused by the initial design and persisted by the requirements for backwards-compatibility. In the last decade, a number of programming languages have chosen JavaScript as the compile target of the language.

Type theory and its application, programming language type systems, is an essential area of study in the design of programming languages. Every high-level programming language features a type system that greatly influences the ways of designing and implementing programs in the language. This thesis examines a group of selected statically-typed programming languages that compile to JavaScript. The core topics of research in this thesis are the motivation for new JS-compiled languages, the type system design of the languages, and the future direction of the JavaScript ecosystem based on the current trends and parallels to other programming ecosystems.

The results of the work include identifying several trends in type systems for the JS ecosystem and the web. These include unsound yet convenient partially inferred type systems for object-oriented and multi-paradigm programming and fully inferred extended Hindley-Milner type systems for primarily functional programming languages. Additionally, different options for the advancement of the programming ecosystem, including type annotations, inference of dynamically typed languages and new compile targets, are explored. Finally, based on the design choices of the languages researched, we provide several recommendations for safe and productive statically typed programming in the JavaScript ecosystem.