/*jshint esnext:true */
/*jshint esnext:true */
Traceur TodoMVC
--------------------
A re-write of the Backbone TodoMVC app using ECMAScript 6
features. Written by Addy Osmani, Pascal Hartig,
Sindre Sorhus, Stephen Sawchuck and Rick Waldron,
with help from Domenic Denicola.
Constant (const
) definitions are block scoped, but their values are read-only.
This means they cannot be re-declared later on. As Backbone's core component
definitions don't need to be modified, we can conbine constants and a pattern
known as 'destructuring' to create shorter aliases for creating Models, Views
and other components, rather than having to use the more verbose Backbone.*
forms we're
used to.
const { Model, View, Collection, Router, LocalStorage } = Backbone;
ES6 modules allow us to define isolated blocks of reusable code without
having to wrap it into an object or closure. Only those functions and
variables we explicitly export
are available to other consumers
and we can just as easily import
functionality from other modules.
It's possible to rename exported values, define modules that are inline
and even declare defaults for import/export.
module TodoApp {
const ENTER_KEY = 13;
const TodoFilter = '';
In JavaScript, we've relied on prototypal inheritance anytime we've needed a class-like system. This has led to overly verbose code using custom types. ES6 changes that by removing the ugly multi-step inheritance patterns we're used to and introducing a minimal class syntax that makes defining classes a lot more terse.
ES6 classes desugar to prototypal inheritance behind the scenes and the only
real change is that there's less typing required for us. Classes are compact
and we can use an 'extend' keyword to implement a new sub-class from a
base-class. Below, we do this to define a Todo
class which extends
Backbone's
Model component.
Our basic Todo model has title
and completed
attributes.
class Todo extends Model {
Note the omission of the 'function' keyword as in ES6 it is entirely optional Default attributes for the todo.
defaults() {
return {
title: '',
completed: false
};
}
Toggle the completed
state of this todo item.
toggle() {
this.save({
completed: !this.get('completed')
});
}
}
The collection of todos is backed by localStorage instead of a remote server.
class TodoList extends Collection {
Specifying a constructor
lets us define the class constructor. Use of the
super
keyword in your constructor lets you call the constructor of a parent
class so that it can inherit all of its properties.
constructor(options) {
super(options);
Reference to this collection's model.
this.model = Todo;
Save all of the todo items under the 'todos'
namespace.
this.localStorage = new LocalStorage('todos-traceur-backbone');
}
Filter down the list of all todo items that are finished.
The fat-arrow (=>
) below is shorthand syntax for an anonymous function
which returns a value. It also doesn't require the function keyword
and the parens are option when there's a single parameter being used.
The value of this is bound to its containing scope, automatically
returning the value of the expression that follows the fat arrow.
completed() {
return this.filter(todo => todo.get('completed'));
}
Filter down the list to only todo items that are still not finished.
remaining() {
return this.without(...this.completed());
}
We keep the Todos in sequential order, despite being saved by unordered GUID in the database. This generates the next order number for new items.
nextOrder() {
if (!this.length) {
return 1;
}
return this.last().get('order') + 1;
}
Todos are sorted by their original insertion order.
comparator(todo) {
return todo.get('order');
}
}
Create our global collection of Todos.
var Todos = new TodoList();
The DOM element for a todo item...
class TodoView extends View {
constructor(options) {
... is a list tag.
this.tagName = 'li';
The TodoView listens for changes to its model, re-rendering. Since there's a one-to-one correspondence between a Todo and a TodoView in this app, we set a direct reference on the model for convenience.
this.model = Todo;
Cache the template function for a single item.
this.template = _.template($('#item-template').html());
this.input = '';
The DOM events specific to an item.
this.events = {
'click .toggle': 'toggleCompleted',
'dblclick label': 'edit',
'click .destroy': 'clear',
'keypress .edit': 'updateOnEnter',
'blur .edit': 'close'
};
super(options);
this.listenTo(this.model, 'change', this.render);
this.listenTo(this.model, 'destroy', this.remove);
this.listenTo(this.model, 'visible', this.toggleVisible);
}
Re-render the contents of the todo item.
render() {
this.$el.html(this.template(this.model.toJSON()));
this.$el.toggleClass('completed', this.model.get('completed'));
this.toggleVisible();
this.input = this.$('.edit');
return this;
}
toggleVisible() {
this.$el.toggleClass('hidden', this.isHidden);
}
get isHidden() {
var isCompleted = this.model.get('completed');
return (// hidden cases only
(!isCompleted && TodoFilter === 'completed') ||
(isCompleted && TodoFilter === 'active')
);
}
Toggle the "completed"
state of the model.
toggleCompleted() {
this.model.toggle();
}
Switch this view into 'editing'
mode, displaying the input field.
edit() {
var value = this.input.val();
this.$el.addClass('editing');
this.input.val(value).focus();
}
Close the 'editing'
mode, saving changes to the todo.
close() {
var title = this.input.val();
if (title) {
this.model.save({ title });
} else {
this.clear();
}
this.$el.removeClass('editing');
}
If you hit enter
, we're through editing the item.
updateOnEnter(e) {
if (e.which === ENTER_KEY) {
this.close();
}
}
Remove the item, destroy the model.
clear() {
this.model.destroy();
}
}
Our overall AppView is the top-level piece of UI.
export class AppView extends View {
constructor() {
Instead of generating a new element, bind to the existing skeleton of the App already present in the HTML.
this.setElement($('#todoapp'), true);
this.statsTemplate = _.template($('#stats-template').html()),
Delegated events for creating new items, and clearing completed ones.
this.events = {
'keypress #new-todo': 'createOnEnter',
'click #clear-completed': 'clearCompleted',
'click #toggle-all': 'toggleAllComplete'
};
At initialization we bind to the relevant events on the Todos
collection, when items are added or changed. Kick things off by
loading any preexisting todos that might be saved in localStorage.
this.allCheckbox = this.$('#toggle-all')[0];
this.$input = this.$('#new-todo');
this.$footer = this.$('#footer');
this.$main = this.$('#main');
this.listenTo(Todos, 'add', this.addOne);
this.listenTo(Todos, 'reset', this.addAll);
this.listenTo(Todos, 'change:completed', this.filterOne);
this.listenTo(Todos, 'filter', this.filterAll);
this.listenTo(Todos, 'all', this.render);
Todos.fetch();
super();
}
Re-rendering the App just means refreshing the statistics -- the rest of the app doesn't change.
render() {
const completed = Todos.completed().length;
const remaining = Todos.remaining().length;
if (Todos.length) {
this.$main.show();
this.$footer.show();
this.$footer.html(
this.statsTemplate({
completed, remaining
})
);
this.$('#filters li a')
.removeClass('selected')
.filter('[href="#/' + (TodoFilter || '') + '"]')
.addClass('selected');
} else {
this.$main.hide();
this.$footer.hide();
}
this.allCheckbox.checked = !remaining;
}
Add a single todo item to the list by creating a view for it, and
appending its element to the <ul>
.
addOne(model) {
const view = new TodoView({ model });
$('#todo-list').append(view.render().el);
}
Add all items in the Todos collection at once.
addAll() {
this.$('#todo-list').html('');
Todos.each(this.addOne, this);
}
filterOne(todo) {
todo.trigger('visible');
}
filterAll() {
Todos.each(this.filterOne, this);
}
Generate the attributes for a new Todo item.
newAttributes() {
return {
title: this.$input.val().trim(),
order: Todos.nextOrder(),
completed: false
};
}
If you hit return in the main input field, create new Todo model, persisting it to localStorage.
createOnEnter(e) {
if (e.which !== ENTER_KEY || !this.$input.val().trim()) {
return;
}
Todos.create(this.newAttributes());
this.$input.val('');
}
Clear all completed todo items, destroying their models.
clearCompleted() {
_.invoke(Todos.completed(), 'destroy');
return false;
}
toggleAllComplete() {
const completed = this.allCheckbox.checked;
Todos.each(todo => todo.save({ completed }));
}
}
export class Filters extends Router {
constructor() {
this.routes = {
'*filter': 'filter'
}
this._bindRoutes();
}
filter(param) {
Set the current filter to be used
TodoFilter = param || '';
Trigger a collection filter event, causing hiding/unhiding of Todo view items
Todos.trigger('filter');
}
}
}
We import the classes we defined in the TodoApp module using the import
keyword. Typically, you would store this module in its own separate file
and import it from there instead, but we're keeping everything in a single
script here for demonstration purposes.
import { AppView, Filters } from TodoApp;
Load the application once the DOM is ready, using jQuery.ready
:
$(() => {
Finally, we kick things off by creating the App.
new AppView();
new Filters();
Backbone.history.start();
});