Question

我创建了一个基于原型的类Person，它打开一个WebSocket连接，并将回调函数定义为原型方法。

因为在回调this内部将引用WebSocket对象，我使用另一个变量来保持Person的{{1}}。但是当我处理多个实例时，变量会被覆盖。

这是一个显示问题的小剪片：

this

如果创建了多个function Person(name){ self = this self.name = name } Person.prototype = { getName : function(){ return self.name }, openConnection : function(host, port){ self.pointCount = 0 self.ws = new WebSocket("ws://" + host + ":" + port) self.ws.onopen = self.onOpenConnection }, onOpenConnection : function() { console.log(this) // prints the websocket console.log(self) // prints the person self.ws.send(self.name) // works only if one person exists } } var p1 = new Person("Jonh") var p2 = new Person("Adam") console.log(p1.getName()) // Prints Adam console.log(p2.getName()) // Prints Adam p1.openConnection("localhost", 7000) // opens connection for p1 p2.openConnection("localhost", 7000) // opens another connection for p1，那么当尝试通过套接字发送消息时，我会收到以下错误：

未捕获错误：INVALID_STATE_ERR：DOM例外11

所以看起来Person是全局定义的，我在回调中尝试获取self的{{1}}的句柄失败了。关于如何实现这一目标的任何建议？

Answer 1

当你这样做时：

self = this

您隐式创建一个全局变量（因为它是全局变量）将对所有实例具有相同的值。局部变量，前面必须有var，let或const，如下所示：

var self = this;
const self = this;
let self = this;

但是，这不是你的解决方案。您需要使用this代替。并且，如果您要为websocket提供回调并且您想要与之关联的人，我建议您只在websocket上添加对Person对象的引用，以便您可以从那里检索它。并且，所有缺少的分号结束每个语句是什么？无论如何，这里有一些固定的代码：

function Person(name){
    this.name = name;
}

Person.prototype = {
    getName : function(){
        return this.name;
    },

    openConnection : function(host, port){
        this.pointCount = 0;
        this.ws = new WebSocket("ws://" + host + ":" + port);
        // save person reference on the web socket
        // so we have access to the person from web socket callbacks
        this.ws.person = this;   
        this.ws.onopen = this.onOpenConnection;
    },

    onOpenConnection : function()   {
        // "this" will be the websocket
        // "this.person" is the person object
        console.log(this); // prints the websocket
        console.log(this.person); // prints the person
        this.send(this.person.name); // works only if one person exists
    }
}

Answer 2

在Javascript中声明变量时，如果你没有放置var，它将被视为全局变量，这会导致你的情况出现问题。

虽然构造函数的行为符合预期，但您可能希望执行以下操作，因此name将保存到您正在创建的Person实例中：

// Constructor
function Person(name){
    // You don't need to reference "self" here. It's already implied.
    this.name = name;
}

此外，在WebSocket.onopen中，“this”从Person的实例更改为WebSocket的实例。您需要保留“Person”才能在WebSocket.onopen中引用它。

// Prototype
Person.prototype = {
    getName : function(){
        // 'this' in this case refers to an instance of Person. 
        // So, when creating John, this.name will be John. 
        return this.name;
    },

    openConnection : function(host, port) {
        // Similar to getName(...), this refers to an instance of Person.
        // In your example, this.pointCount is NOT shared between John and Adam
        this.pointCount = 0;
        this.ws = new WebSocket("ws://" + host + (port ? ':' + port : ''));

        // In WebSocket.onopen below, you're working with a new scope, so you 
        // won't have access to 'this' as the Person anymore. You need to save 
        // 'this' somewhere, so you can reference it in the new scope.
        // *****
        var self = this;   

        this.ws.onopen = function() {
            // In this function, a new scope has been created. 'this' no 
            // longer refers to John/Adam (The instance of Person), but to 
            // WebSocket instead.

            console.log(this); // 'this' references the WebSocket instance
            console.log(self); // 'self' references the 'self' in the outer 
                               // scope. See *****

            // Since this = WebSocket in this scope, all we need to do
            // is this.send(...). If you'd like to obtain the refer
            // to the instance of the Person you worked with, you can
            // use the 'self' variable
            this.send(self.name); 
        };
    }
};

希望这有帮助！这是一个JSFiddle：http://jsfiddle.net/WFdbe/

Answer 3

self = this

您创建一个全局变量，这就是您的代码被破坏的原因。

同样尝试在原型中引用self不起作用，请使用this

function Person(name){
    this.name = name
}

Person.prototype = {
    openConnection : function(host, port){
        this.pointCount = 0
        this.ws = new WebSocket("ws://" + host + ":" + port)
        this.ws.onopen = this.onOpenConnection.bind(this)
    },
    constructor: Person,    
    onOpenConnection : function()   {
        console.log(this) // prints the person
        this.ws.send(this.name) // works only if one person exists
    }
}

javascript：带回调的原型和'this'

3 个答案: