emberscript

+computed firstName, lastName
fullName: (key, value) ->
  if arguments.length == 2 and value
    name = value.split(' ')
    @firstName = name[0]
    @lastName = name.slice(1).join(' ')

  if @firstName or @lastName
    "#{@firstName} #{@lastName}"
  else
    null

emberscript-generated-js

fullName: Ember.computed(function (key, value) {
  var name;
  if (get$(arguments, 'length') === 2 && value) {
    name = value.split(' ');
    set$(this, 'firstName', name[0]);
    set$(this, 'lastName', name.slice(1).join(' '));
  }
  if (get$(this, 'firstName') || get$(this, 'lastName')) {
    return '' + get$(this, 'firstName') + ' ' + get$(this, 'lastName');
  } else {
    return null;
  }
}).property('firstName', 'lastName')f

plain-js

fullName: function(key, value) {
  if (arguments.length === 2 && value) {
    var name = value.split(' ');
    this.set('firstName', name[0]);
    this.set('lastName', name.slice(1).join(' '));
  }

  var firstName = this.get('firstName') || '';
  var lastName = this.get('lastName') || '';

  if (firstName || lastName) {
    return firstName + ' ' + lastName;
  } else {
    return null;
  }
}.property('firstName', 'lastName')