Question

您好我已阅读documentation和几个blog posts，我仍然不了解.bind（this）在下面的代码中发生了什么。

代码对我有用，但我不想理解发生的事情

如果我从下面的代码中删除.bind（this）会怎么样？
什么是绑定什么？

    

import Ember from 'ember';

// Since I've defined my url in environment.js I can do this

import ENV from '../config/environment';
var ref = new window.Firebase(ENV.firebase);

export default {
    name: 'session',

    // Run the initializer after the store is ready
    after: 'store',

    initialize: function(container, app) {  
        // session object is nested here as we need access to the container to get the store
        var session = Ember.Object.extend({

            // initial state
            authed: false,

            init: function() {
                // get access to the ember data store
                this.store = container.lookup('store:main');
                // on init try to login
                ref.onAuth(function(authData) {

                    // Not authenticated
                    if (!authData) {
                        this.set('authed', false);
                        this.set('authData', null);
                        this.set('user', null);
                        return false;
                    }

                    // Authenticated
                    this.set('authed', true);
                    this.set('authData', authData);
                    this.afterAuthentication(authData.uid);
                ***}.bind(this));***
            },

            // Call this from your Ember templates
            login: function(provider) {
                this._loginWithPopup(provider);
            },

            // Call this from your Ember templates
            logout: function() {
                ref.unauth();
            },

            // Default login method
            _loginWithPopup: function(provider) {
                var _this = this;
                // Ember.debug('logging in with popup');
                ref.authWithOAuthPopup(provider, function(error, authData) {
                    if (error) {
                        if (error.code === "TRANSPORT_UNAVAILABLE") {
                            // fall-back to browser redirects, and pick up the session
                            // automatically when we come back to the origin page
                            _this._loginWithRedirect(provider);
                        }
                    } else if (authData) {
                        // we're good!
                        // this will automatically call the on ref.onAuth method inside init()
                    }
                });
            },

            // Alternative login with redirect (needed for Chrome on iOS)
            _loginWithRedirect: function(provider) {
                ref.authWithOAuthRedirect(provider, function(error, authData) {
                    if (error) {

                    } else if (authData) {
                        // we're good!
                        // this will automatically call the on ref.onAuth method inside init()
                    }
                });
            },

            // Runs after authentication
            // It either sets a new or already exisiting user
            afterAuthentication: function(userId) {
                var _this = this;

                // See if the user exists using native Firebase because of EmberFire problem with "id already in use"
                ref.child('users').child(userId).once('value', function(snapshot) {
                    var exists = (snapshot.val() !== null);
                    userExistsCallback(userId, exists);
                });

                // Do the right thing depending on whether the user exists
                function userExistsCallback(userId, exists) {
                    if (exists) {
                        _this.existingUser(userId);
                    } else {
                        _this.createUser(userId);
                    }
                }
            },

            // Existing user
            existingUser: function(userId) {
                var _this = this;
                this.store.find('user', userId).then(function(user) {
                    _this.set('user', user);
                ***}.bind(this));***
            },

            // Create a new user
            createUser: function(userId) {
                var _this = this;

                this.get('store').createRecord('user', {
                    id: userId,
                    provider: this.get('authData.provider'),
                    name: this.get('authData.facebook.displayName') || this.get('authData.google.displayName'),
                    email: this.get('authData.facebook.email') || this.get('authData.google.email'),
                    created: new Date().getTime()
                }).save().then(function(user){

                    // Proceed with the newly create user
                    _this.set('user', user);
                });
            },

            // This is the last step in a successful authentication
            // Set the user (either new or existing)
            afterUser: function(user) { 
                this.set('user', user);
            }
        });

        // Register and inject the 'session' initializer into all controllers and routes
        app.register('session:main', session);
        app.inject('route', 'session', 'session:main');
        app.inject('controller', 'session', 'session:main');
    }
}; <code>

Answer 1

您在回调函数上使用.bind（this）。这意味着，函数内部的this通常会引用调用函数的上下文（这是JavaScript，与上下文中的其他语言不同）。您想要 this来引用当前上下文。这就是.bind(this)的作用：它确保使用当前上下文（而不是默认上下文）调用回调函数。

什么是Ember.bind以及它是如何工作的？

1 个答案: