recast

A sufficiently-motivated engineer could do this today by setting a different formatter in their editor than in their pre-commit hook. Then they need only activate the formatter in their editor as they edit, and ensure pre-commit hooks run as they commit. This saves you the trouble of authoring a separate programming language, or finding a way to preserve all of the niceties of the original syntax and formatting that wouldn't directly translate to an AST (like how many newlines are after a particular stanza or function). Case in point: Recast (https://github.com/benjamn/recast) is of particular interest with regards to JS/TS in this vein, because it does preserve a lot of the spirit of the source in its conception of the AST. But also last time I used it (couple years ago now) it would explode on any code with an emoji in it. It's genuinel

This is a powerful idea! If I understand Monocle's use case, JS has similar AST parsing and code generation tools that are used broadly. There may be some ideas to learn from that community. JS AST specs: estree [0] and babel's AST [1] Parsers: babel [2], acorn [3], or espree [4] Transformers: babel, recast [5], or jscodeshift [6] Codegen: babel or escodegen [7] [0] https://github.com/estree/estree [1] https://babeljs.io/docs/en/babel-parser#output [2] https://github.com/babel/babel [3] https://github.com/acornjs/acorn [4] https://github.com/eslint/espree [5] https://github.com/benjamn/recast [6] https://github.com/facebook/jscodeshift [7] https://github.com/estools/escodegen

This project is dead, but writing a Babel transform using something like https://github.com/benjamn/recast is easy and fun!

Personally I've moved away from the TypeScript compiler and towards the betas of `babel@7` and `@babel/preset-typescript` (https://www.npmjs.com/package/@babel/preset-typescript). It seems to be faster and there is better integration with `jest`, `rollup`, various css-in-js libraries and (maybe in future?) `create-react-app`. (I still run `tslint` and `typescript` in the background for type-checking and linting. And I've written a tiny CLI to generate flat `index.d.ts` files to share my packages.) The one thing I still miss about JavaScript is the possibility of writing codemods to speed-up upgrades. Unfortunately, in order for `jscodeshift` to support TypeScript, I think there would need to be some further work on `recast` (https://github.com/benjamn/recast/issues/424). Hopefully the TypeScript team will continue to work closely with the

I'm surprised that doesn't exist. When I did a lot of Perl in a team environment, we used perltidy. Helpful since Perl does little to encourage uniformity. It could take any sort of style in, and produce any sort of style out. Things like K&R blocks vs Allman-style blocks, tabs vs spaces, line wrapping, cuddled/not-cuddled else, etc. http://perltidy.sourceforge.net/stylekey.html Edit: this looks pretty close to the same thing for JavaScript. Missing some style options, and not command line driven, but the general idea seems close: https://github.com/benjamn/recast/blob/master/README.md

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.

jscodeshift is primarily a wrapper around recast. Recast takes care of all the printing. It's smart enough to reuse the original source code for AST nodes that haven't been changed. As for formatting, there are some options to influence the pretty printer, but not a lot [1]. It will infer things like indentation from the existing source code. I'm not sure right now how it handles long lines. Whenever we run into issues with the printer, we just create a PR to fix it. Getting automatic code formatting right is apparently quite hard. There are dedicated tools for this, such as https://github.com/millermedeiros/esformatter . [1]: https://github.com/benjamn/recast/blob/master/lib/options.js