Transpilation

Transpilation, short for source-to-source compilation, is the process of converting code written in one high-level programming language into another high-level language at a similar level of abstraction. The goal is to preserve behavior and structure as much as possible while changing the language and often the target runtime environment. This contrasts with traditional compilation, which typically targets lower-level code such as machine language or bytecode, and with interpretation, which executes code directly without generating an alternative source form.

A transpiler typically performs parsing, an abstract syntax tree transformation, and code generation. It may adapt or erase types, insert runtime libraries, or rely on polyfills to emulate features not present in the target language. The resulting code is intended to run in environments that support the target language or its ecosystem, often within the same runtime family (for example, JavaScript running in a web browser).

Common uses include enabling developers to write code in a preferred or newer language and run it in environments that only support an older or different language, facilitating backward compatibility or cross-language workflows. Transpilers are also used during language migrations and to leverage ecosystem tooling across languages.

Examples include TypeScript to JavaScript, CoffeeScript to JavaScript, and Babel-based workflows that convert modern JavaScript syntax (ECMAScript 2015 and later) into backward-compatible JavaScript. Other languages, such as Elm, Kotlin, or Scala, may compile to JavaScript, while some transpilation pipelines target intermediate representations for platforms like WebAssembly.

Limitations arise when a source language’s features do not map cleanly to the target language, which may require compromises, runtime libraries, or polyfills. Transpilation remains a foundational technique for modern cross-language development and web tooling.