Understanding JavaScript engines
As mentioned in the introduction to this chapter, a JavaScript engine is responsible for interpreting JavaScript and/or transforming it into machine code, so that the device can execute it.
The first JavaScript engines were simple interpreters that simply processed the statements and ensured the execution. The code was just executed like it was written. This has changed a lot.
Modern JS engines provide a lot of optimization features. The most discussed is just-in-time (JIT) compilation, which is implemented by all modern JS engines.
Compiled languages such as C are compiled before the execution of the code. In this compile step, the transformation to machine language is done as well as a lot of optimization steps. This creates an output that is extremely performant.
Just-in-time compilation means that the code is compiled while it runs. This means the just-in-time compiler does not know all the code while it compiles. This makes code optimization...
