example.coffee

class example
  constructor() ->
    @leftPanel = 5
  
  #This is bad
  @deletePaneCallback:(id) ->
      console.log 'leftPane:' + @leftPanel  #This will be undefined
  
  #this is good
  @deletePaneCallback2: (id) =>
      cosole.log 'leftPane:' + @leftPanel # This will be 5
      
  @consumeBottomDock: (@bottomDock) ->
      @bottomDock.onDidDeletePane @deletePaneCallback
      @bottomDock.onDidDeletePane @deletePaneCallback2
    

example.js

var example = function() {
  this.leftPanel = 5;
  
  this.deletePaneCallback(id) {
    console.log('leftPanel:' + this.leftPanel); //This will be undefined
  }
  
  
  this.consumeBottomDock: (@bottomDock) ->
    //This is the same as @deletePaneCallback
    this.bottomDock.onDidDeletePane(this.deletePaneCallback); //This will be undefined
    
    //This is the same as @deleteCallback2
    this.bottomDock.onDidDeletePane(this.deletePaneCallback.bind(this)); //This will be 5
}