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Emacs Settings for JavaScript

Unlike other language development, JavaScript, for me, has two components, a front-end, browser-based interface, as well as a back-end, server-side interface through Node.

JS2 Mode

I like the extras found in Steve Yegge’s js2-mode.

(use-package js2-mode
  :ensure t
  :init
  (setq js-basic-indent 2)
  (setq-default js2-basic-indent 2
                js2-basic-offset 2
                js2-auto-indent-p t
                js2-cleanup-whitespace t
                js2-enter-indents-newline t
                js2-indent-on-enter-key t
                js2-global-externs (list "window" "module" "require" "buster" "sinon" "assert" "refute" "setTimeout" "clearTimeout" "setInterval" "clearInterval" "location" "__dirname" "console" "JSON" "jQuery" "$"))

  (add-hook 'js2-mode-hook
            (lambda ()
              (push '("function" . ?ƒ) prettify-symbols-alist)))

  (add-to-list 'auto-mode-alist '("\\.js$" . js2-mode)))

Color defined variables with color-identifiers-mode:

(use-package color-identifiers-mode
    :ensure t
    :init
      (add-hook 'js2-mode-hook 'color-identifiers-mode))

Flycheck and JSHint

While editing JavaScript is baked into Emacs, it is quite important to have flycheck validate the source based on jshint, and eslint. Let’s prefer eslint:

(add-hook 'js2-mode-hook
          (lambda () (flycheck-select-checker "javascript-eslint")))

Now load and edit a JavaScript file, like jshint-code-test.js.

Tern

The Tern project is a JavaScript analyzer that can be used to improve the JavaScript integration with editors like Emacs.

(use-package tern
   :ensure t
   :init (add-hook 'js2-mode-hook (lambda () (tern-mode t)))
   :config
     (use-package company-tern
        :ensure t
        :init (add-to-list 'company-backends 'company-tern)))

The following additional keys are bound:

M-.
Jump to the definition of the thing under the cursor.
M-,
Brings you back to last place you were when you pressed M-..
C-c C-r
Rename the variable under the cursor.
C-c C-c
Find the type of the thing under the cursor.
C-c C-d
Find docs of the thing under the cursor. Press again to open the associated URL (if any).

Refactoring JavaScript

The js2-refactor mode should start with C-c . and then a two-letter mnemonic shortcut.

  • ef is extract-function: Extracts the marked expressions out into a new named function.
  • em is extract-method: Extracts the marked expressions out into a new named method in an object literal.
  • ip is introduce-parameter: Changes the marked expression to a parameter in a local function.
  • lp is localize-parameter: Changes a parameter to a local var in a local function.
  • eo is expand-object: Converts a one line object literal to multiline.
  • co is contract-object: Converts a multiline object literal to one line.
  • eu is expand-function: Converts a one line function to multiline (expecting semicolons as statement delimiters).
  • cu is contract-function: Converts a multiline function to one line (expecting semicolons as statement delimiters).
  • ea is expand-array: Converts a one line array to multiline.
  • ca is contract-array: Converts a multiline array to one line.
  • wi is wrap-buffer-in-iife: Wraps the entire buffer in an immediately invoked function expression
  • ig is inject-global-in-iife: Creates a shortcut for a marked global by injecting it in the wrapping immediately invoked function expression
  • ag is add-to-globals-annotation: Creates a /*global */ annotation if it is missing, and adds the var at point to it.
  • ev is extract-var: Takes a marked expression and replaces it with a var.
  • iv is inline-var: Replaces all instances of a variable with its initial value.
  • rv is rename-var: Renames the variable on point and all occurrences in its lexical scope.
  • vt is var-to-this: Changes local var a to be this.a instead.
  • ao is arguments-to-object: Replaces arguments to a function call with an object literal of named arguments. Requires yasnippets.
  • 3i is ternary-to-if: Converts ternary operator to if-statement.
  • sv is split-var-declaration: Splits a var with multiple vars declared, into several var statements.
  • uw is unwrap: Replaces the parent statement with the selected region.
(use-package js2-refactor
  :ensure t
  :init   (add-hook 'js2-mode-hook 'js2-refactor-mode)
  :config (js2r-add-keybindings-with-prefix "C-c ."))

Skewer

I also configure Skewer for my HTML and CSS files, we need to do the same for JavaScript:

(use-package skewer-mode
   :ensure t
   :init (add-hook 'js2-mode-hook 'skewer-mode))

Kick things off with run-skewer, and then:

C-x C-e
`skewer-eval-last-expression’
C-M-x
`skewer-eval-defun’
C-c C-k
`skewer-load-buffer’

Coffee

Using the coffee-mode for CoffeeScript file.

(use-package coffee-mode
   :ensure t
   :init
   (setq-default coffee-tab-width 2))

Need to remember the following keybindings:

Return
Insert newline and indent line
C-c C-<, backtab
Indent line or region to left
C-c C->
Indent line or region to right
A-r, C-c C-k
Compile buffer to JavaScript
A-R
Compile content of region to JavaScript
A-M-r, C-c C-z
Run CoffeeScript REPL
C-c C-l
Send this line to REPL buffer
C-c C-r
Send content of region to REPL buffer
C-c C-b
Send content of buffer to REPL buffer
C-c C-o C-s
Enable coffee-cos-mode
(use-package ob-coffee
   :ensure t)

Technical Artifacts

Make sure that we can simply require this library.

(provide 'init-javascript)

Before you can build this on a new system, make sure that you put the cursor over any of these properties, and hit: C-c C-c