javascript - View 的哪个函数首先被执行？初始化还是渲染？

Question

我在以下代码中插入了三个 console.log，该代码来自教程 Your First Backbone.js App .

我的问题是:为什么 console.log(this.el) 显示元素的 innerHtml 已经“渲染”，但 console.log('render running!') 之后打印消息？

View 的哪个函数首先被执行？初始化还是渲染？

$(function(){

    // Create a model for the services
    var Service = Backbone.Model.extend({

        // Will contain three attributes.
        // These are their default values

        defaults:{
            title: 'My service',
            price: 100,
            checked: false
        },

        // Helper function for checking/unchecking a service
        toggle: function(){
            this.set('checked', !this.get('checked'));
        }
    });


    // Create a collection of services
    var ServiceList = Backbone.Collection.extend({

        // Will hold objects of the Service model
        model: Service,

        // Return an array only with the checked services
        getChecked: function(){
            return this.where({checked:true});
        }
    });

    // Prefill the collection with a number of services.
    var services = new ServiceList([
        new Service({ title: 'web development', price: 200}),
        new Service({ title: 'web design', price: 250}),
        new Service({ title: 'photography', price: 100}),
        new Service({ title: 'coffee drinking', price: 10})
        // Add more here
    ]);

    // This view turns a Service model into HTML
    var ServiceView = Backbone.View.extend({
        tagName: 'div',

        events:{
            'click': 'toggleService'
        },

        initialize: function(){

            // Set up event listeners. The change backbone event
            // is raised when a property changes (like the checked field)
            console.log(this);
            console.log(this.el);

            this.listenTo(this.model, 'change', this.render);
        },

        render: function(){

            // Create the HTML
            console.log("render runs!");

            this.$el.html('<input type="checkbox" value="1" name="' + this.model.get('title') + '" /> ' + this.model.get('title') + '<span>$' + this.model.get('price') + '</span>');
            this.$('input').prop('checked', this.model.get('checked'));

            // Returning the object is a good practice
            // that makes chaining possible
            return this;
        },

        toggleService: function(){
            this.model.toggle();
        }
    });

    // The main view of the application
    var App = Backbone.View.extend({

        // Base the view on an existing element
        el: $('#main'),

        initialize: function(){

            // Cache these selectors
            this.total = $('#total span');
            this.list = $('#services');


            // Listen for the change event on the collection.
            // This is equivalent to listening on every one of the 
            // service objects in the collection.
            this.listenTo(services, 'change', this.render);


            // Create views for every one of the services in the
            // collection and add them to the page

            services.each(function(service){

                var view = new ServiceView({ model: service });
                this.list.append(view.render().el);

            }, this);   // "this" is the context in the callback
        },

        render: function(){

            // Calculate the total order amount by agregating
            // the prices of only the checked elements

            var total = 0;

            _.each(services.getChecked(), function(elem){
                total += elem.get('price');
            });

            // Update the total price
            this.total.text('$'+total);

            return this;

        }

    });

    new App();

});

控制台输出如下:

child {cid: "view7", model: child, $el: init[1], el: div}
<div>
<input type="checkbox" value="1" name="web development"> web development
<span>$200</span></div>
render runs!

Answer 1

initialize 始终首先调用，因为它位于默认 Backbone 的 View 构造函数内。

render 每当您手动调用它时都会被调用。

services.each(function(service) {

    // ServiceView 'initialize' is called here.
    var view = new ServiceView({ model: service });
    // ServiceView 'render' is called here.
    this.list.append(view.render().el);

}, this);

为什么控制台在渲染前显示el？

事实上，控制台在渲染之前并不显示该元素，而是在您在控制台中检查它时对其进行评估。

这是一个简单的例子:

var myObject = {};

console.log(myObject);

myObject.test = "value";

如果您必须猜测，您会说记录了一个空对象，并且您不会完全错误。

小蓝!说:

Object value at left was snapshotted when logged, value below was evaluated just now.

正如“mu太短”所说，

the console contains live references and doesn't copy anything. So when you get to the console to look at this.el, it shows you what this.el is right now rather than what it was when console.log(this.el) was evaluated.