atom/docs/packages/creating_a_package.md

Creating Packages

Let's take a look at creating our first package.

Atom has a command you can enter that'll create a package for you: package-generator:generate. Otherwise, you can hit meta-p, and start typing "Package Generator." Once you activate this package, it'll ask you for a name for your new package. Let's call ours changer.

Now, changer is going to have a default set of folders and files created for us. Hit meta-R to reload Atom, then hit meta-p and start typing "Changer." You'll see a new Changer:Toggle command which, if selected, pops up a new message. So far, so good!

In order to demonstrate the capabilities of Atom and its API, our Changer plugin is going to do two things:

1. It'll show only modified files in the file tree
2. It'll append a new pane to the editor with some information about the modified files

Let's get started!

Changing Keybindings and Commands

Since Changer is primarily concerned with the file tree, let's write a keybinding that works only when the tree is focused. Instead of using the default toggle, our keybinding executes a new command called magic.

keymaps/changer.cson can easily become this:

'.tree-view-scroller':
  'ctrl-V': 'changer:magic'

Notice that the keybinding is called ctrl-V--that's actually ctrl-shift-v. You can use capital letters to denote using shift for your binding.

.tree-view-scroller represents the parent container for the tree view. Keybindings only work within the context of where they're entered. For example, hitting ctrl-V anywhere other than tree won't do anything. You can map to body if you want to scope to anywhere in Atom, or just .editor for the editor portion.

To bind keybindings to a command, we'll use the rootView.command method. This takes a command name and executes a function in the code. For example:

rootView.command "changer:magic", => @magic()

It's common practice to namespace your commands with your package name, and separate it with a colon (:). Rename the existing toggle method to magic to get the binding to work.

Reload the editor, click on the tree, hit your keybinding, and...nothing happens! What the heck?!

Open up the package.json file, and notice the key that says activationEvents. Basically, this tells Atom to not load a package until it hears a certain event. Let's change the event to changer:magic and reload the editor.

Hitting the key binding on the tree now works!

Working with styles

The next step is to hide elements in the tree that aren't modified. To do that, we'll first try and get a list of files that have not changed.

All packages are able to use jQuery in their code. In fact, we have a list of some of the bundled libraries Atom provides by default.

Let's bring in jQuery:

$ = require 'jquery'

Now, we can query the tree to get us a list of every file that wasn't modified:

magic: ->
  $('ol.entries li').each (i, el) ->
    if !$(el).hasClass("modified")
      console.log el

You can access the dev console by hitting alt-meta-i. When we execute the changer:magic command, the browser console lists the items that are not being modified. Let's add a class to each of these elements called hide-me:

magic: ->
  $('ol.entries li').each (i, el) ->
    if !$(el).hasClass("modified")
      $(el).addClass("hide-me")

With our newly added class, we can manipulate the visibility of the elements with a simple stylesheet. Open up changer.css in the stylesheets directory, and add a single entry:

ol.entries .hide-me {
  display: none;
}

Refresh atom, and run the changer command. You'll see all the non-changed files disappear from the tree. There are a number of ways you can get the list back; let's just naively iterate over the same elements and remove the class:

magic: ->
  $('ol.entries li').each (i, el) ->
    if !$(el).hasClass("modified")
      if !$(el).hasClass("hide-me")
        $(el).addClass("hide-me")
      else
        $(el).removeClass("hide-me")

Creating a New Pane

The next goal of this package is to append a pane to the Atom editor that lists some information about the modified files.

To do that, we're going to first create a new class method called content. Every package that extends from the View class can provide an optional class method called content. The content method constructs the DOM that your package uses as its UI. The principals of content are built entirely on SpacePen, which we'll touch upon only briefly here.

Our display will simply be an unordered list of the file names, and their modified times. Let's start by carving out a div to hold the filenames:

@content: ->
  @div class: 'modified-files-container', =>
    @ul class: 'modified-files-list', outlet: 'modifiedFilesList', =>
      @li 'Test'
      @li 'Test2'

You can add any HTML5 attribute you like. outlet names the variable your package can uses to manipulate the element directly. The fat pipe (=>) indicates that the next set are nested children.

We'll add one more line to magic to make this pane appear:

rootView.vertical.append(this)

If you hit the key command, you'll see a box appear right underneath the editor. Success!

Before we populate this, let's apply some logic to toggle the pane off and on, just like we did with the tree view:

# toggles the pane
if @hasParent()
  rootView.vertical.children().last().remove()
else
  rootView.vertical.append(this)

There are about a hundred different ways to toggle a pane on and off, and this might not be the most efficient one. If you know your package needs to be toggled on and off more freely, it might be better to draw the UI during the initialization, then immediately call hide() on the element to remove it from the view. You can then swap between show() and hide(), and instead of forcing Atom to add and remove the element as we're doing here, it'll just set a CSS property to control your package's visibility.

You might have noticed that our two li elements aren't showing up. Let's set a color on them so that they pop. Open up changer.css and add this CSS:

ul.modified-files-list {
  color: white;
}

Refresh Atom, hit the key combo, and see your brilliantly white test list.

Calling Node.js Code

Since Atom is built on top of Node.js, you can call any of its libraries, including other modules that your package requires.

We'll iterate through our resulting tree, and construct the path to our modified file based on its depth in the tree:

path = require 'path'

# ...

modifiedFiles = []
# for each single entry...
$('ol.entries li.file.modified span.name').each (i, el) ->
  filePath = []
  # ...grab its name...
  filePath.unshift($(el).text())

  # ... then find its parent directories, and grab their names
  parents = $(el).parents('.directory.modified')
  parents.each (i, el) ->
    filePath.unshift($(el).find('div.header span.name').eq(0).text())

  modifiedFilePath = path.join(project.rootDirectory.path, filePath.join(path.sep))
  modifiedFiles.push modifiedFilePath

modifiedFiles is an array containing a list of our modified files. We're also using the node.js path library to get the proper directory separator for our system.

Let's remove the two @li elements we added in @content, so that we can populate our modifiedFilesList with real information. We'll do that by iterating over modifiedFiles, accessing a file's last modified time, and appending it to modifiedFilesList:

# toggles the pane
if @hasParent()
  rootView.vertical.children().last().remove()
else
  for file in modifiedFiles
    stat = fs.lstatSync(file)
    mtime = stat.mtime
    @modifiedFilesList.append("<li>#{file} - Modified at #{mtime}")
  rootView.vertical.append(this)

When you toggle the modified files list, your pane is now populated with the filenames and modified times of files in your project. You might notice that subsequent calls to this command reduplicate information. We could provide an elegant way of rechecking files already in the list, but for this demonstration, we'll just clear the modifiedFilesList each time it's closed:

# toggles the pane
if @hasParent()
  @modifiedFilesList.empty()
  rootView.vertical.children().last().remove()
else
  for file in modifiedFiles
    stat = fs.lstatSync(file)
    mtime = stat.mtime
    @modifiedFilesList.append("<li>#{file} - Modified at #{mtime}")
  rootView.vertical.append(this)