Cython vs Scala.js

Cython is a free compiler for Python and the extended Cython language, used to create C extensions for Python. It translates source code into C or C++ that can be built as Python extension modules. Optional static type declarations can help produce more efficient C, while declared C and C++ types let Python code call existing C or C++ code. Cython supports source-level debugging across Python, Cython and C, and the project describes uses including wrapping external libraries, embedding CPython in applications and speeding up Python code with C modules. It can work with multidimensional NumPy arrays and integrate with low-level libraries and applications. Installation is available through pip, and some scientific Python distributions bundle it. A C compiler is required, with installation guidance for Linux, macOS and Windows. The project describes compatibility with major C and C++ compilers for CPython 3.8 and later, and characterizes PyPy support as mostly usable. Limited API and free-threading CPython support in Cython 3.1 are experimental. Cython is available under the Apache 2.0 License.

Scala.js is a Scala-to-JavaScript compiler for building applications that run in browsers, Node.js, and serverless environments. The project also states that WebAssembly support is stable. Scala's strong typing can catch mistakes such as mixing strings and numbers or using misspelled method names, while editor support can flag type errors and show inline details about methods, arguments, return types, and documentation. The project describes incremental compilation with a 1–2 second turnaround; generated JavaScript for a full application starts at 45 kB gzipped. Scala.js can use JavaScript libraries and APIs through statically or dynamically typed access. Listed library integrations include React, Angular, Vue, Three.js, and Chart.js. Build tool options include sbt, scala-cli, Mill, and Gradle with a Scala.js plugin. Tutorials list Scala development tools and Node.js as prerequisites and recommend VS Code with Metals. Scala.js is free and distributed under the Apache License 2.0. Documentation points users to community support through Discord and Stack Overflow. The 1.22.0 release is not entirely backward source compatible with 1.21.x.