JavaScript

Summary

JavaScript (ˈdʒɑːvəskrɪpt), often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. As of 2023, 98.7% of websites use JavaScript on the client side for webpage behavior, often incorporating third-party libraries. All major web browsers have a dedicated JavaScript engine to execute the code on users' devices. JavaScript is a high-level, often just-in-time compiled language that conforms to the ECMAScript standard. It has dynamic typing, prototype-based object-orientation, and first-class functions. It is multi-paradigm, supporting event-driven, functional, and imperative programming styles. It has application programming interfaces (APIs) for working with text, dates, regular expressions, standard data structures, and the Document Object Model (DOM). The ECMAScript standard does not include any input/output (I/O), such as networking, storage, or graphics facilities. In practice, the web browser or other run

Official source

https://en.wikipedia.org/wiki/JavaScript

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Scala.js: Type-Directed Interoperability with Dynamically Typed Languages

Sébastien Jean R Doeraene

Interoperability between statically typed and dynamically typed languages is increasingly important, as can be witnessed by the many statically typed languages targeting JavaScript. Interoperating with both the object-oriented and functional features of JavaScript is essential, if only to manipulate the DOM, yet existing languages have very poor support for this. We present Scala.js, a dialect of Scala compiling to JavaScript. Its interoperability system is based on a powerful and intuitive framework for type-directed interoperability with dynamically typed languages. The framework combines facade types for JavaScript values; user-defined, implicit, type-directed cross-language conversions; and a Dynamic type building on facade types and implicit conversions. It accommodates both the functional and object-oriented features of Scala and JavaScript, and provides very natural interoperability between the two languages. It is expressive enough to represent the DOM and jQuery APIs, among others, both in its statically typed and dynamically typed flavors.

2013

Cross-Platform Language Design

Sébastien Jean R Doeraene

Programming languages are increasingly compiled to multiple runtimes, each featuring their own rich structures such as their object model. Furthermore, they need to interact with other languages targeting said runtimes. A language targeting only one runtime can be designed to tailor its semantics to those of that runtime, for easy interoperability with other languages. However, in a language targeting multiple runtimes with differing semantics, it is difficult to cater to each of them while retaining a common behavior across runtimes. We call \emph{cross-platform language} a language that aims at being both \emph{portable} across platforms and \emph{interoperable} with each target platform. Portability is the ability for a program or a library to cross-compile for multiple platforms, and behave the same way on all of them. Interoperability is the ability to communicate with other languages on the same platform. While many cross-compiling languages focus on one of these two properties---only adding support for the other one as an afterthought---, languages that are designed from the ground up to support both are rare. In this thesis, we present the design of Scala.js, the dialect of Scala targeting the JavaScript platform, which turned Scala into a cross-platform language. On the one hand, Scala programs can be cross-compiled for the JVM and JavaScript with portable semantics. On the other hand, whereas Scala/JVM interoperates with Java, Scala.js interoperates with JavaScript, allowing to use any JavaScript library. Along the dissertation, we give insights that can be transferred to the design of other cross-platform languages, although with a bias towards those targeting the JVM and JavaScript. The first and most obvious challenge is to reconcile the static nature of Scala's object model with JavaScript's dynamic one. Besides the ability to mutate a class hierarchy at run-time in JavaScript, there are fundamental differences between the two models, in particular the difference between compile-time overloading and run-time overloading. We discuss how such semantic mismatches can live in harmony within the language. The second challenge is to obtain good performance from a language where interoperability with a dynamic and unknown part of the program is pervasive. To that end, we design and specify an intermediate representation (IR) with first-class support for dynamically typed interoperability features in addition to statically typed JVM-style operations. Despite its tight integration with the open world of JavaScript, most of the IR can be considered as a closed world where advanced whole-program optimizations can be performed. The performance of the overall system is evaluated and shown to be competitive with hand-written JavaScript, and even with Scala/JVM in some cases.

EPFL2018

Have you ever wondered what is the secret sauce of Scala.js? What defines Scala.js, above all else, is the overarching will to make it cross-platform. A cross-platform language is both portable-most source code cross-compiles and behaves the same way on multiple platforms-and interoperable-code written in that language can interoperate with other languages on the target platforms. Most multi-platform languages are designed with one of those two properties in mind, and only address the other one as an afterthought. This results in poor integration, difficulty to write portable code, or even the impossibility to use some platform-specific libraries. This talk shows how Scala.js was designed as a cross-platform language. We show how portability and interoperability drive every design decision, from which language feature to include to performance considerations. We state a criteria of completeness for interoperability, and show how Scala.js satisfies it (with the exception of one JavaScript language feature, still work-in-progress). We give insights about what features are critical for portability, and which ones can be relaxed in the name of performance. In particular, we stress the importance of the ecosystem of libraries: existing assumptions in the ecosystem can force the language designer into reproducing behaviors of Scala/JVM, even when they are accidental. As a practical exercise, we study the main language changes that made it into Scala.js 1.x wrt. 0.6.x-as well as possible future developments-and how they fit into the cross-platform language design methodology.

ASSOC COMPUTING MACHINERY2018

Cross-Platform Language Design

Sébastien Jean R Doeraene

EPFL2018