Understanding how WebAssembly works

Let's first explore how JavaScript and WebAssembly are executed inside the JavaScript engine.

Understanding JavaScript execution inside the JavaScript engine

The JavaScript engine first fetches the complete JavaScript file (note that the engine has to wait until the entire file is downloaded/loaded).

Note

The bigger the JavaScript file, the longer it takes to load. It doesn't matter how fast your JavaScript engine is or how efficient your code is. If your JavaScript file is huge (that is, greater than 170 KB), then your application is going to be slow at loading time.

Figure 3.1 – JavaScript execution inside the JavaScript engine

Once loaded, the JavaScript is parsed into abstract syntax trees (ASTs). This phase is called parse. Since JavaScript is both an interpreted and compiled language, the JavaScript engine kickstarts the execution after parsing. The interpreter executes the code faster...