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when I edit javascript, I'm usually actually editing someone else's code. Is there a way to dynamically set the value of js-indent-level from a .eslintrc file?

  • Considering that .eslintrc doesn't have to be a JSON, getting that information out will be hacky. An easy solution could be to bind running --fix to a key, or you could look into something like EditorConfig. – DoMiNeLa10 Nov 13 '18 at 20:50
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I know nothing about eslint or it's rc file, but TMTOWTDI as the Perl folks are fond of saying. Here's is how I solved a similar problem for myself using shell-command-to-string. I needed to get the version of CMake that was installed on whatever system I happened to be on.

(defvar cmake-mode-cmake-version
  (let (l)
    (setq l (shell-command-to-string
             (concat cmake-mode-cmake-executable " --version")))
    (string-match  (rx bow
                       (one-or-more digit)
                       "."
                       (one-or-more digit)
                       (zero-or-more "." (one-or-more digit))
                       eow)
                   l)
    (match-string 0 l))
 "The version of CMake from `cmake-mode-cmake-executable'")

First, we define a new variable cmake-mode-cmake-version. Then we run shell-command-to-string with a string that I concat together. At this point you're going to want to use something like "grep indent-level .eslint". (Again, don't know anything about eslint. Just working off the cuff here). Next, in string-match we look for a version string using a regex constructed with the rx package. With match-string we return the result of the last match (the one we just did with string-match), and cmake-mode-cmake-version now contains something like '3.11.1'. It's not the most lispy code, but hopefully it's clear.

Now, you could of course forego the concats, and the string-matchs, etc. Assuming your rc file is list of "things = values" then we could imagine something like:

(eval-after-load "js-mode"
  (defvar my/eslint-indent
    '(let (l)
      (setq l (shell-command-to-string "grep indent-level .eslintrc | egrep -o '\\d+$' | tr -d '\\n'"))
      l)
   "The indent level from .eslintrc"))
  (setq js-indent-level my/eslint-indent))

where we set js-indent-level after loading our chosen JavaScript mode. Of course this is just an example, and you'll have to tweak it some for your own needs.

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