Google's V8 engine is designed solely for running JavaScript code. Unfortunately, it doesn't have the ability to comprehend TypeScript, a superset of JavaScript with additional type information. Therefore, any TypeScript code must undergo a transformation process to be translated into JavaScript. This enables the V8 engine to understand and execute it effectively.
Deno, on the other hand, employs a combination of tools, specifically the TSC (TypeScript Compiler) and SWC (Super-fast Web Compiler), to handle both TypeScript and JavaScript files. When the need arises for type-checking, Deno turns to Microsoft's TSC compiler, which not only performs the conversion to JavaScript but also checks for type-related errors. However, if type-checking isn't necessary, Deno leverages the SWC compiler for an exceptionally swift transpilation process. The reason behind this preference is that TSC, being implemented in JavaScript, tends to be sluggish compared to the performance of SWC.
SWC, the Super-fast Web Compiler, distinguishes itself by its speed and efficiency. Crafted using the Rust programming language, SWC functions as a swift TypeScript/JavaScript compiler. It takes in JavaScript or TypeScript files that incorporate modern features like async-await, and in turn, generates JavaScript code that is compatible with older web browsers. This transformation is crucial for ensuring that the code can run on a wide range of browsers, catering to varying levels of support for newer language features.
Deno capitalizes on the capabilities of SWC to seamlessly convert TypeScript files into JavaScript. Deno's compatibility with the latest ECMAScript specifications eliminates the need to convert JavaScript files into an older style for compatibility reasons. By default, SWC is selective in its processing—it primarily handles TypeScript files, leaving JavaScript files untouched, unless there's a specific request to alter them.
For more in-depth insights into SWC, you can refer to their official website: https://swc.rs/. This resource provides comprehensive information about the compiler's features, functionality, and how to best utilize it for your programming needs.