jscodeshift

I'd strongly suggest diving into compilers if you've never studied the subject. Learning a bit on the subject unlocks a ton of incredibly useful skills. That knowledge helps you implement stuff like autocomplete, linters, syntax highlighting, etc. The Super Tiny Compiler [0] is a very gentle introduction to the subject. It's great because it helps you quickly develop an initial mental model. To give an everyday usage example: I've used jscodeshift [1] many times to safely refactor large amounts of code. In one case, I quickly migrated a project's test assertion library to an alternative which the team agreed was superior. This tool is also typically used by the react team in order to provide a smooth migration path whenever they make changes to the public API. [0] https://github.com/thejameskyle/the-super-tiny-compiler [1] https://github.

I find the idea of https://github.com/facebook/jscodeshift to be really useful. I've started writing small scripts using the TypeScript parser as a library to make meaningful improvements in our codebase. Since JavaScript is valid TypeScript syntax the scripts work on both. For example, I wrote a small script to change var to let or const when possible. It uses the AST to check scoping rules and to check if a variable is ever reassigned. Writing scripts like this is way more effective than doing it by hand.

Facebook also maintains a JS codemod tool that React uses: https://github.com/facebook/jscodeshift

For JavaScript we have https://github.com/estree/estree as our JS AST spec for parsers like esprima, acorn, babylon (under a config flag), etc. JSCS (https://github.com/jscs-dev/node-jscs) (now merged with ESLint) started a CST project as well https://github.com/cst/cst to help deal with autoformatting by adding whitespace type nodes. Currently the community has a lot of interest in https://github.com/jlongster/prettier which just simply reprints the file from scratch in a consistent way (posted in https://news.ycombinator.com/item?id=13365470). We also have https://github.com/benjamn/recast to help source to source transformations and https://github.com/facebook/jscodeshift.