babel-handbook VS esprima

For more information about building Babel plugins, check the Kent's Babel Handbook or this awesome Babel handbook by Jamie.

Babel does this by compiling down JavaScript code written with the latest standards into a version that will work everywhere today. This process is known as source-to-source compiling, also known as transpiring. Source: Jamie Kyle

I'll be honest, my approach to getting used to working with ASTs is a bit weird, but it worked for me. For some reason the thought of working with the TypeScript AST sounds really attractive to me. I'm sure most people recommend to start deep diving into babel first before getting used to working with an AST with the TypeScript compiler, but I started it the other way around. There is a great library called ts-morph that focuses on making it easier for developers to work with the TypeScript compiler. Learning hands on with ts-morph while getting used to their compiler api made babel much easier to understand without ever touching babel.

Those videos gave me a base for the task but I needed more sources to achieve it, so I read a lot of source code for other libraries built with babel-plugin-macros, read the plugin's authoring documentation and Jamie Kyle's Babel Handbook.

If you want to learn more about parsing, reading the code of an actual recursive parser might be a better idea. Esprima is a decent place to start if you're interested in JS grammar. Then you can look at the babel handbook to learn more about AST transformations. From there, the literature gets quite a bit more heavy. If you get this far and are willing to push further, you'll probably want to grab yourself a copy of the dragon book at a minimum.

Babel handbook

I'm particularly fond of Firecracker, but it’s a bit of work to set up, so if you cannot afford the time yet, you want to be on the safe side, do a combination of static analysis and time-boxing execution. You can use esprima to parse the code and check for any malicious act.

Focusing again on ESLint, the parser used by the linter is called Espree. This is an in-house parser built by the ESLint folks to fully support ECMAScript 6 and JSX on top of the already existing Esprima. The Espree module provide APIs for both tokenization and parsing that you can easily test out.

For TypeScript we have used AST transforms from their compiler API, and for plain JavaScript we did a similar thing using ESPrima. This helped us implement some simple optimizations like stream fusion (combining .filter and .map into a single operation) or avoiding extra object allocations in vector math, which led to nice performance improvements in code that does heavy computation (we process large amounts of data on the server and store results of physics simulations).

I used ESPrima, but any parser would do in this case. I then wrote a simple function to extract all "atomic" non-boolean expressions from it.

AST is an acronym for Abstract Syntax Tree. It's the way to represent code in a format that tools can understand. Usually in form of tree data structure. We will use AST in the format of an Esprima, which is a JavaScript parser that outputs AST.

esprima

Create an AST: Esprima

The thread was originally about CRA vs Vite size on disk (or implicitly, if we're applying it to real world applications, network cost in CI job startup times). And like I said, surrogate pairs don't apply to ASCII.

See this[0] for reference. Note how the first byte must fall within a certain range in order to signal being a surrogate pair. This fact is taken advantage of by JS parsers to make parsing of ASCII code faster by special casing that range, since checking for a valid character in the entire unicode range is quite a bit more expensive[1].

[0] https://github.com/jquery/esprima/blob/0911ad869928fd218371b...

[1] https://github.com/jquery/esprima/blob/0911ad869928fd218371b...

If you want to learn more about parsing, reading the code of an actual recursive parser might be a better idea. Esprima is a decent place to start if you're interested in JS grammar. Then you can look at the babel handbook to learn more about AST transformations. From there, the literature gets quite a bit more heavy. If you get this far and are willing to push further, you'll probably want to grab yourself a copy of the dragon book at a minimum.