#+TITLE: JavaScript layer

#+TAGS: general|js|layer|multi-paradigm|programming

[[file:img/javascript.png]]

* Table of Contents                     :TOC_5_gh:noexport:
- [[#description][Description]]
  - [[#features][Features:]]
- [[#install][Install]]
  - [[#web-beautify][web-beautify]]
  - [[#prettier][prettier]]
  - [[#import-js][import-js]]
  - [[#choosing-a-backend][Choosing a backend]]
  - [[#choosing-a-formatter][Choosing a formatter]]
  - [[#format-buffer-before-saving][Format buffer before saving]]
- [[#backends][Backends]]
  - [[#tern][Tern]]
  - [[#language-server-protocol][Language Server Protocol]]
    - [[#typescript][TypeScript]]
    - [[#flow][Flow]]
    - [[#debugger-dap-integration][Debugger (dap integration)]]
- [[#configuration][Configuration]]
  - [[#indentation][Indentation]]
  - [[#repl][REPL]]
    - [[#browser-based-repl][Browser based REPL]]
    - [[#server-based-repl][Server based REPL]]
  - [[#node][Node]]
    - [[#node-modules][Node Modules]]
    - [[#node-externs][Node Externs]]
  - [[#flowtypescript][Flow/Typescript]]
- [[#key-bindings][Key bindings]]
  - [[#js2-mode][js2-mode]]
  - [[#folding-js2-mode][Folding (js2-mode)]]
  - [[#importing-import-js][Importing (import-js)]]
  - [[#refactoring-js2-refactor][Refactoring (js2-refactor)]]
    - [[#documentation-js-doc][Documentation (js-doc)]]
  - [[#browser-based-repl-skewer-mode][Browser based REPL (skewer-mode)]]
  - [[#server-based-repl-nodejs-repl][Server based REPL (nodejs-repl)]]
  - [[#debugger-dap-mode][debugger (dap mode)]]

* Description
This layer adds support for the JavaScript language using [[https://github.com/mooz/js2-mode][js2-mode]].

** Features:
- Multiple backends support: Tern and LSP
- Smart code folding
- Refactoring: done using [[https://github.com/magnars/js2-refactor.el][js2-refactor]].
- Auto-completion and documentation
- Browser based REPL available via [[https://github.com/skeeto/skewer-mode][skewer-mode]] and [[https://github.com/pandeiro/livid-mode][livid-mode]]
- Server based REPL with [[https://github.com/abicky/nodejs-repl.el][nodejs-repl]]
- Formatting with [[https://github.com/yasuyk/web-beautify][web-beautify]] or [[https://github.com/prettier/prettier][prettier]]
- Interactive debugger using [[https://github.com/emacs-lsp/dap-mode][dap-mode]]
- Display Flow & Typescript type information

* Install
To use this configuration layer, add it to your =~/.spacemacs=. You will need to
add =javascript= to the existing =dotspacemacs-configuration-layers= list in
this file.

To enable the importing helper, install the =ImportJS=:

#+BEGIN_SRC sh
  $ npm install -g import-js
#+END_SRC

To activate error checking using flycheck, install one of the [[http://www.flycheck.org/en/latest/languages.html#javascript][available linters]]
such as =ESLint= or =JSHint=:

#+BEGIN_SRC sh
  $ npm install -g eslint
  # or
  $ npm install -g jshint
#+END_SRC

If you install these in non-standard locations, then add the following to your
=dotspacemacs/user-init= function:

#+BEGIN_SRC elisp
  (add-to-list 'exec-path "/path/to/node/bins" t)
#+END_SRC

** web-beautify
See [[file:../../+tools/web-beautify/README.org][web-beautify layer]] documentation.

** prettier
See [[file:../../+tools/prettier/README.org][prettier layer]] documentation.

** import-js
See [[file:../../+tools/import-js/README.org][import-js layer]] documentation.

To enable it, set the layer variable =javascript-import-tool=:

#+BEGIN_SRC elisp
  (javascript :variables javascript-import-tool 'import-js)
#+END_SRC

** Choosing a backend
To choose a default backend set the layer variable =javascript-backend=:

#+BEGIN_SRC elisp
  (javascript :variables javascript-backend 'tern)
#+END_SRC

Alternatively the =lsp= backend will be automatically chosen if the layer =lsp=
is used and you did not specify any value for =javascript-backend=.

Backend can be chosen on a per project basis using directory local variables
(files named =.dir-locals.el= at the root of a project), an example to use the
=lsp= backend:

#+BEGIN_SRC elisp
  ;;; Directory Local Variables
  ;;; For more information see (info "(emacs) Directory Variables")

  ((js2-mode (javascript-backend . lsp)))
#+END_SRC

When =lsp= is set as the backend, but you don't want to use lsp as the linter,
set the variable =javascript-lsp-linter= to =nil=.

#+BEGIN_SRC elisp
  (javascript :variables
              javascript-backend 'lsp
              javascript-lsp-linter nil)
#+END_SRC

** Choosing a formatter
To choose a formatter, set the layer variable =javascript-fmt-tool=:

#+BEGIN_SRC elisp
  (javascript :variables javascript-fmt-tool 'web-beautify)
#+END_SRC

The formatter can be chosen on a per project basis using directory local
variables (files named =.dir-locals.el= at the root of a project). For example
to use the =prettier= formatter:

#+BEGIN_SRC elisp
  ;;; Directory Local Variables
  ;;; For more information see (info "(emacs) Directory Variables")

  ((js2-mode (javascript-fmt-tool . prettier)))
#+END_SRC

*Note:* you can easily add a directory local variable with ~SPC f v d~.

You can choose formatting tool:

#+BEGIN_SRC elisp
  (setq-default dotspacemacs-configuration-layers '(
    (javascript :variables
                javascript-fmt-tool 'prettier)))
#+END_SRC

Default is =’web-beautify=.

** Format buffer before saving
#+BEGIN_SRC elisp
  (javascript :variables javascript-fmt-on-save t)
#+END_SRC

* Backends
** Tern
See [[file:../../+tools/tern/README.org][tern layer]] documentation.

** Language Server Protocol
To use an LSP server with JavaScript, add it as a =javascript-backend= to your
=~/.spacemacs=.

#+BEGIN_SRC emacs-lisp
  (setq-default dotspacemacs-configuration-layers
                '((javascript :variables
                              javascript-backend 'lsp)))
#+END_SRC

*** TypeScript
You have to install =typescript-language-server= (recommended) or
=javascript-typescript-langserver= language server packages via

#+BEGIN_SRC sh
  npm i -g typescript typescript-language-server
#+END_SRC

or

#+BEGIN_SRC sh
  npm i -g typescript javascript-typescript-langserver
#+END_SRC

*** Flow
You have to install =flow-bin=.

#+BEGIN_SRC sh
  npm i -g flow-bin
#+END_SRC

Or, if you'd rather use a locally-installed =flow-bin= from your project's
node_modules directory, see the [[#node-modules][node-add-modules-path setting]].

*** Debugger (dap integration)
To install the debug adapter you may run =M-x dap-firefox-setup= or
=M-x dap-chrome-setup= if you are using Linux or download it manually from
[[https://marketplace.visualstudio.com/items?itemName=hbenl.vscode-firefox-debug][Firefox Debug Adapter]] or [[https://marketplace.visualstudio.com/items?itemName=msjsdiag.debugger-for-chrome][Chrome Debug Adapter]] and adjust
=dap-firefox-debug-path= or =dap-chrome-debug-path=. For usage instructions
refer to [[https://github.com/emacs-lsp/dap-mode][dap-mode]] readme.

* Configuration
** Indentation
To change how js2-mode indents code, set the variable =js2-basic-offset=, as
such:

#+BEGIN_SRC emacs-lisp
  (setq-default js2-basic-offset 2)
#+END_SRC

or when adding the =javascript= configuration layer:

#+BEGIN_SRC emacs-lisp
  (javascript :variables js2-basic-offset 2)
#+END_SRC

Similarly, to change how js-mode indents JSON files, set the variable
=js-indent-level=, as such:

#+BEGIN_SRC emacs-lisp
  (setq-default js-indent-level 2)
#+END_SRC

or when adding the =javascript= configuration layer:

#+BEGIN_SRC emacs-lisp
  (javascript :variables js-indent-level 2)
#+END_SRC

** REPL
*** Browser based REPL
To use the browser based REPL set the =javascript-repl= variable as shown below:

#+BEGIN_SRC elisp
  (setq-default dotspacemacs-configuration-layers
    '((javascript :variables javascript-repl `skewer)))
#+END_SRC

In addition you need a running httpd server and a page loaded
with skewer. If a blank page serves your needs, just use the run-skewer command
in your javascript buffer. If you want to inject it in your own page, follow
[[https://github.com/skeeto/skewer-mode#skewering-with-cors][these instructions]] (install the Greasemonkey script and then click the triangle
in the top-right corner - if it turns green, you're good to go).

*** Server based REPL
To use the server based REPL set the =javascript-repl= variable as shown below:

#+BEGIN_SRC elisp
  (setq-default dotspacemacs-configuration-layers
    '((javascript :variables javascript-repl `nodejs)))
#+END_SRC

In addition install nodejs and make sure that =node= is in the path.

** Node
*** Node Modules
If you would like =node_modules/.bin= to be automatically added to the buffer
local =exec_path=, e.g. to support project local eslint installations, set the
=node-add-modules-path= variable in the =javascript= config section. Note that
doing this [[https://stackoverflow.com/questions/9679932#comment33532258_9683472][introduces a security risk]]:

#+BEGIN_SRC elisp
  (setq-default dotspacemacs-configuration-layers
    '((javascript :variables node-add-modules-path t)))
#+END_SRC

*** Node Externs
If you want =js2-mode= to presume =node= variables are defined by the host
system (for completion purposes /i.a./) set the =js2-include-node-exters=
variable to =t= in the =javascript= config section:

#+BEGIN_SRC elisp
  (setq-default dotspacemacs-configuration-layers
    '((javascript :variables js2-include-node-externs t)))
#+END_SRC

** Flow/Typescript
   Enable the [[Language Server Protocol][lsp]] backend to view type information, jump to declarations, and more.

   js2-mode is sometimes confused by the type syntax, so you may wish to disable their
   parse warnings:

#+BEGIN_SRC emacs-lisp
  (javascript :variables javascript-backend 'lsp
              js2-mode-show-strict-warnings nil
              js2-mode-show-parse-errors nil)
#+END_SRC

* Key bindings
** js2-mode

| Key binding | Description                          |
|-------------+--------------------------------------|
| ~SPC m w~   | toggle js2-mode warnings and errors  |
| ~%~         | jump between blockswith [[https://github.com/redguardtoo/evil-matchit][evil-matchit]] |

** Folding (js2-mode)

| Key binding | Description              |
|-------------+--------------------------|
| ~SPC m z c~ | hide element             |
| ~SPC m z o~ | show element             |
| ~SPC m z r~ | show all element         |
| ~SPC m z e~ | toggle hide/show element |
| ~SPC m z F~ | toggle hide functions    |
| ~SPC m z C~ | toggle hide comments     |

** Importing (import-js)

| Key binding | Description                                                         |
|-------------+---------------------------------------------------------------------|
| ~SPC m i i~ | Import the module for the variable under the cursor                 |
| ~SPC m i f~ | Import any missing modules and remove any modules that are not used |
| ~SPC m g i~ | Go to the module of the variable under cursor                       |

** Refactoring (js2-refactor)
Bindings should match the plain emacs assignments.

| Key binding   | Description                                                                                                    |
|---------------+----------------------------------------------------------------------------------------------------------------|
| ~SPC m k~     | deletes to the end of the line, but does not cross semantic boundaries                                         |
| ~SPC m r 3 i~ | converts ternary operator to if-statement                                                                      |
| ~SPC m r a g~ | creates a =/* global */= annotation if it is missing, and adds var to point to it                              |
| ~SPC m r a o~ | replaces arguments to a function call with an object literal of named arguments                                |
| ~SPC m r b a~ | moves the last child out of current function, if-statement, for-loop or while-loop                             |
| ~SPC m r c a~ | converts a multiline array to one line                                                                         |
| ~SPC m r c o~ | converts a multiline object literal to one line                                                                |
| ~SPC m r c u~ | converts a multiline function to one line (expecting semicolons as statement delimiters)                       |
| ~SPC m r e a~ | converts a one line array to multiline                                                                         |
| ~SPC m r e f~ | extracts the marked expressions into a new named function                                                      |
| ~SPC m r e m~ | extracts the marked expressions out into a new method in an object literal                                     |
| ~SPC m r e o~ | converts a one line object literal to multiline                                                                |
| ~SPC m r e u~ | converts a one line function to multiline (expecting semicolons as statement delimiters)                       |
| ~SPC m r e v~ | takes a marked expression and replaces it with a var                                                           |
| ~SPC m r i g~ | creates a shortcut for a marked global by injecting it in the wrapping immediately invoked function expression |
| ~SPC m r i p~ | changes the marked expression to a parameter in a local function                                               |
| ~SPC m r i v~ | replaces all instances of a variable with its initial value                                                    |
| ~SPC m r l p~ | changes a parameter to a local var in a local function                                                         |
| ~SPC m r l t~ | adds a console.log statement for what is at point (or region)                                                  |
| ~SPC m r r v~ | renames the variable on point and all occurrences in its lexical scope                                         |
| ~SPC m r s l~ | moves the next statement into current function, if-statement, for-loop, while-loop                             |
| ~SPC m r s s~ | splits a =String=                                                                                              |
| ~SPC m r s v~ | splits a =var= with multiple vars declared into several =var= statements                                       |
| ~SPC m r t f~ | toggle between function declaration and function expression                                                    |
| ~SPC m r u w~ | replaces the parent statement with the selected region                                                         |
| ~SPC m r v t~ | changes local =var a= to be =this.a= instead                                                                   |
| ~SPC m r w i~ | wraps the entire buffer in an immediately invoked function expression                                          |
| ~SPC m r w l~ | wraps the region in a for-loop                                                                                 |
| ~SPC m x m j~ | move line down, while keeping commas correctly placed                                                          |
| ~SPC m x m k~ | move line up, while keeping commas correctly placed                                                            |

*** Documentation (js-doc)
You can check more [[https://github.com/mooz/js-doc/][here]]

| Key binding   | Description                           |
|---------------+---------------------------------------|
| ~SPC m r d b~ | insert JSDoc comment for current file |
| ~SPC m r d f~ | insert JSDoc comment for function     |
| ~SPC m r d t~ | insert tag to comment                 |
| ~SPC m r d h~ | show list of available jsdoc tags     |

** Browser based REPL (skewer-mode)

| Key binding | Description                                                      |
|-------------+------------------------------------------------------------------|
| ~SPC m e e~ | evaluates the last expression                                    |
| ~SPC m e E~ | evaluates and inserts the result of the last expression at point |

| Key binding | Description                                                                        |
|-------------+------------------------------------------------------------------------------------|
| ~SPC m T l~ | Toggle live evaluation of whole buffer in REPL on buffer changes                   |
| ~SPC m s b~ | send current buffer contents to the skewer REPL                                    |
| ~SPC m s B~ | send current buffer contents to the skewer REPL and switch to it in insert state   |
| ~SPC m s f~ | send current function at point to the skewer REPL                                  |
| ~SPC m s F~ | send current function at point to the skewer REPL and switch to it in insert state |
| ~SPC m s i~ | starts/switch to the skewer REPL                                                   |
| ~SPC m s r~ | send current region to the skewer REPL                                             |
| ~SPC m s R~ | send current region to the skewer REPL and switch to it in insert state            |
| ~SPC m s s~ | switch to REPL                                                                     |

** Server based REPL (nodejs-repl)

| Key binding | Description                                                        |
|-------------+--------------------------------------------------------------------|
| ~SPC m s i~ | Switch to NodeJS REPL if one has been started, otherwise start one |
| ~SPC m s e~ | Send last expression to NodeJS REPL                                |
| ~SPC m s E~ | Send last expression to NodeJS REPL and switch to REPL             |
| ~SPC m s b~ | Send current buffer to NodeJS REPL                                 |
| ~SPC m s B~ | Send current buffer to NodeJS REPL and switch to REPL              |
| ~SPC m s l~ | Send current line to NodeJS REPL                                   |
| ~SPC m s L~ | Send current line to NodeJS REPL and switch to REPL                |
| ~SPC m s r~ | Send active region to NodeJS REPL                                  |
| ~SPC m s R~ | Send active region to NodeJS REPL and switch to REPL               |
| ~SPC m s s~ | switch to REPL                                                     |

** debugger (dap mode)
Using the =dap= layer you'll get access to all the DAP key bindings, see the
complete list of key bindings on the [[https://github.com/syl20bnr/spacemacs/tree/develop/layers/%2Btools/dap#key-bindings][dap layer description]].