# Initial Emacs Setup for React/ReactNative

(Cross posted to the Cyrus Innovation Blog)

It looks likely that I’ll be doing some ReactNative work soon so I took some time to start setting up my Emacs environment. All my relevant setup can be found in the init-react.el file in my GitHub dotfiles repository. This is likely to change so the previous link may not match the code below. The code below matches specifically the initial version (59e7728).

Hereinbelow I will add more annotation to those already found in that file along with snippets of code.

The first thing that needed to be set up was a mode for React code. React code files can mix Javascript with HTML markup and it does not appear that js-mode (the built-in JavaScript mode) handles that. After a short Googling it looks like web-mode is a mode that can handle it. After some brief testing it does appear to work reasonably. It appears that the React/ReactNative community has not decided to use *.js or *.jsx as the extension for the code files and since web-mode appears to handle JavaScript just fine I chose to use it in all cases.

(add-to-list 'auto-mode-alist '("\\.jsx?\$" . web-mode))


The next thing I wanted to get set up was a linter. I thought this especially important as React uses an ES6 dialect of JavaScript which I am not entirely familiar with yet and a linter can help me “do the right thing”. With a suggestion from a coworker (who has done some React work) I chose ESLint with the AirBnB configuration settings. These defaults prompted me to standardize on two spaces for indentation. (Setting js-indent-level as js-mode is still in use for JSON files.)

  (setq web-mode-markup-indent-offset 2
web-mode-css-indent-offset 2
web-mode-code-indent-offset 2)
(setq js-indent-level 2)


Setting up the linter to run via flycheck took a small amount of work since I don’t like to install project specific tools globally. (I know that this is contrary to current mores, but I have been tripped up by global vs. local installations before so I shy away from them when I can.)

First I needed to integrate NVM with Emacs so that Emacs could run ESLint at all.

(require 'nvm)
(nvm-use (caar (last (nvm--installed-versions))))


(The choice to use the last version found is totally arbitrary. If and when I get more versions of Node.js on my machine I’ll have to make a more careful choice.)

Next I hooked into projectile to look for a locally installed ESLint and use it if found. The projectile-after-switch-project-hook functions are called after Projectile has switched directories to the project so one can simply check the project for the desired file.

(add-hook 'projectile-after-switch-project-hook 'mjs/setup-local-eslint)

(defun mjs/setup-local-eslint ()
"If ESLint found in node_modules directory - use that for flycheck.
Intended for use in PROJECTILE-AFTER-SWITCH-PROJECT-HOOK."
(interactive)
(let ((local-eslint (expand-file-name "./node_modules/.bin/eslint")))
(setq flycheck-javascript-eslint-executable
(and (file-exists-p local-eslint) local-eslint))))


(Note: the function is interactive because I found at least a few times I was looking at a JavaScript file which I had come to not via projectile. By making it interactive lets me use it manually in the rare case I need to.)

Flycheck’s ESLint integration is limited to only certain modes and web-mode is not one of them so I needed to add that to the white-list of modes

  (with-eval-after-load 'flycheck
(push 'web-mode (flycheck-checker-get 'javascript-eslint 'modes))))


With that I can easily write React/ReactNative code with all the bells and whistles I like.

Later I will add support for building and testing I’m sure. But first I need to determine what building & testing in a ReactNative environment will even look like.

emacsreactreactnative