// Defining current user role ("guest" by default)
Role.current = 'admin';

// or
Role.current = ['user', 'moderator'];

// or
var CurrentUser = require('my-current-user-instance');
Role.current = function() {
  return CurrentUser.roles;
}

// Defining roles with entity->action mapping
Role.define('user', {
  books: {
    read: true,
    update: function(book) {
      return book && book.authorId === CurrentUser.id
    }
  }
});

// Inheriting existing models
Role.define('admin', 'user', {
  books: {
    update: true
  }
});

// After that you're able to use "can" helper to check if current user's role is allowed to
// perform actions on passed entities.
// E.g. somewhere in code:

if (Role.can('read', 'books')) {
  ...
}

// or

var book = books.get(1);

if (Role.can('update', 'books', book)) {
  ...
}

// or somewhere in Backbone.Router or whatever router that has 'before' filter

... 
before: {
  'books/new': function() {
    if (!Role.can('create', 'books')) {
      this.navigate('/home');
      return false;
    }
  }
}
...

Handlebars.registerHelper('can', function() {
  var abilityArgs = _.initial(arguments),
    able = Role.can.apply(null, abilityArgs),
    options = _.last(arguments);

  return able ? options.fn(this) : options.inverse(this);
});