espree VS babel-handbook

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.

Why do we then have other JavaScript parsers like babel parser, swc parser, acorn, espree and the likes since JavaScript engines have their own internal parsers?

How does ESLint work? ESLint uses Espree for Javascript parsing. It uses an AST to evaluate patterns in code. It does all this before runtime.. meaning, without running your Javascript code it will find the bugs, syntax and stylistic errors.

ESLint doesn't process the code into the compiler phases, rather it provides an option to let you specify a Parser. By default, ESLint uses Espree which essentially converts JS source code to AST data structure, so in case you want to write a rule targeting TypeScript source code, you'll need to specify a different parser in your .eslintrc.json configuration file, same applies for different file extension, for HTML you might use this or creating your own parser!

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