Why do we need WebAssembly?

JavaScript has been around for a long time. It has evolved from a little scripting language that allowed bells and whistles to be added to a web page, to a sprawling JIT compiled language with a massive ecosystem that can be used to write fully fledged applications. Today, JavaScript is doing a lot of things that were probably never imagined when it was created by Netscape in 1995. JavaScript is an interpreted language, meaning that it must be parsed, compiled, and optimized on the fly. JavaScript is also a dynamically typed language, which creates headaches for an optimizer.

Franziska Hinkelmann, a member of the Chrome V8 team, gave a great talk at the Web Rebels 2017 conference where she discusses all the performance improvements made to JavaScript over the past 20 years, as well as the difficulties they had in squeezing every bit of performance imaginable out of the JavaScript V8 engine: https://youtu.be/ihANrJ1Po0w.

WebAssembly solves a lot of the problems created by JavaScript and its long history in the browser. Because the JavaScript engine is already in bytecode format, it does not need to run a parser, which removes a significant bottleneck in the execution of our application. This design also allows the JavaScript engine to know what data types it is dealing with at all times. The bytecode makes optimization a lot easier. The format allows multiple threads in the browsers to work on compiling and optimizing different parts of the code at the same time.

For a detailed explanation of what is happening when the Chrome V8 engine is parsing code, please refer to this video from the JSConf EU 2017, in which Marja Hölttä (who works on the Chrome V8 tool) goes into more detail than you ever imagined you wanted to learn about parsing JavaScript: https://www.youtube.com/watch?v=Fg7niTmNNLg&t=123s.

WebAssembly is not a high-level programming language, but a binary file with opcodes for a virtual machine. Currently, it is considered to be in an MVP stage of development. The technology is still in its infancy, but even now it offers notable performance and file size benefits for many use cases, such as game development. Because of the current limitations of WebAssembly, we have only two choices for languages to use for its development—C/C++ or Rust. The long-term plan for WebAssembly is to support a wide selection of programming languages for its development. If I wanted to write at the lowest level of abstraction, I could write everything in Web Assembly Text (WAT), but WAT was developed as a language to support debugging and testing and was not intended to be used by developers for writing applications.

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