[removed] prototypes with callbacks and 'this'

Question

I\'ve create a prototype based class Person that opens a WebSocket connection and defines callback functions as prototype methods.

Because inside the ca

Answer 1

When declaring variables in Javascript, if you don't put a var in front, it'll be treated as a global variable, which causes some problem in your case.

While the constructor is behaving as expected, you may want to do the following instead, so name is saved to the instance of Person you are creating:

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

In addition, in WebSocket.onopen, 'this' changes from the instance of a Person to the instance of a WebSocket. You'll need to preserve the 'Person' in order to reference it inside WebSocket.onopen.

// 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); 
        };
    }
};

Hope this helps! Here's a JSFiddle to go with it: http://jsfiddle.net/WFdbe/