Hands-On Game Development with WebAssembly

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Will WebAssembly replace JavaScript?

The short answer to this question is not anytime soon. At present, WebAssembly is still in its MVP stage. At this stage, the number of use cases is limited to applications where WebAssembly has limited back and forth with the JavaScript and the Document Object Model (DOM). WebAssembly is not currently able to directly interact with the DOM, and Emscripten uses JavaScript "glue code" to make that interaction work. That interaction will probably change soon, possibly by the time you are reading this, but in the next few years, WebAssembly will need additional features to increase the number of possible use cases.

WebAssembly is not a "feature complete" platform. Currently, it cannot be used with any languages that require GC. That will change and, eventually, almost all strongly typed languages will target WebAssembly. In addition, WebAssembly will soon become tightly integrated with JavaScript, allowing frameworks such as React, Vue, and Angular to begin replacing significant amounts of their JavaScript code with WebAssembly without impacting the application programming interface (API). The React team is currently working on this to improve the performance of React.

In the long run, it is possible that JavaScript may compile into WebAssembly. For technical reasons, this is a very long way off. Not only does JavaScript require a GC (not currently supported), but because of its dynamic nature, JavaScript also requires a runtime profiler to optimize. Therefore, JavaScript would produce very poorly optimized code, or significant modifications would be needed to support strict typing. It is more likely that a language, such as TypeScript, will add features that allow it to compile into WebAssembly.

The AssemblyScript project in development on GitHub is working on a TypeScript-to-WebAssembly compiler. This project creates JavaScript and uses Binaryen to compile that JavaScript into WebAssembly. How AssemblyScript handles the problem of garbage collection is unclear. For more information, refer to https://github.com/AssemblyScript/assemblyscript.

JavaScript is currently ubiquitous on the web; there are a tremendous number of libraries and frameworks developed in JavaScript. Even if there were an army of developers eager to rewrite the entire web in C++ or Rust, WebAssembly is not yet ready to replace these JavaScript libraries and frameworks. The browser makers have put immense efforts into making JavaScript run (relatively) fast, so JavaScript will probably remain as the standard scripting language for the web. The web will always need a scripting language, and countless developers have already put in the work to make JavaScript that scripting language, so it seems unlikely that JavaScript will ever go away.

There is, however, a need for a compiled format for the web that WebAssembly is likely to fulfill. Compiled code may be a niche on the web at the moment, but it is a standard just about everywhere else. As WebAssembly approaches feature-complete status, it will offer more choices and better performance than JavaScript, and businesses, frameworks, and libraries will gradually migrate toward it.