How to define the prototype of an object in a constructor in JavaScript?

Question

I'm to creating an object constructor with an object as one of it's properties, and want to add methods to that object's prototype.

Defining it like so doesn't work because the object is instantiated from an object literal and not from a constructor:

 function Resource (options) {
    this.self = this;
    this.options = options || {};

    .. other options. ...
    
    // service object that I want to add functions to its prototype
    this.service = {
        request: new XMLHttpRequest(),
        requestMethod: options.requestMethod ||'GET',
    },
    // using prototype actually creates an object called prototype 
    // as a property of the service object.
    this.service.prototype = {
        dataToNode: function(element, parent, data){
            var toAppend = document.createElement(element);
            toAppend.innerHTML = data;
            return parent.appendChild(toAppend);
        },
}

Cutting to the chase and using __proto__ like so works, but __proto__ is depreciated.

How can I add to the objects prototype without using `proto`?

function Resource (options) {
    this.self = this;
    this.options = options || {};

    .. other options. ...
    
    // service object that I want to add functions to its prototype
    this.service = {
        request: new XMLHttpRequest(),
        requestMethod: options.requestMethod ||'GET',
    },
    // using __proto__ works but its deprciated
    this.service.__proto__ = {
        dataToNode: function(element, parent, data){
            var toAppend = document.createElement(element);
            toAppend.innerHTML = data;
            return parent.appendChild(toAppend);
        },
}

Your use of __proto__ is entirely replacing the object's prototype. Are you sure that's what you want? Why not just make a separate constructor instead of using Object literal syntax? — cookie monster
– cookie monster, Commented Apr 21, 2014 at 20:40
@cookiemonster its not what I want, thanks for clarifying. I just want to add functionality to the prototype. — agconti
– agconti, Commented Apr 21, 2014 at 20:41
Then you could do Object.getPrototypeOf(this.service).newMethod = ..., but you'll be adding the method to the prototype of an plain object, which means you'll be adding to Object.prototype. A separate constructor will be safer. — cookie monster
– cookie monster, Commented Apr 21, 2014 at 20:42
Or do: this.service = Object.create({dataToNode: function(element, parent, data) {...}});, which will set the object you pass as the prototype of a new object returned. Then put the request and requestMethod properties on this.service. — cookie monster
– cookie monster, Commented Apr 21, 2014 at 20:46

Esailija · Accepted Answer · 2014-04-21 20:40:15Z

2

function Service(options) {
    this.request = new XMLHttpRequest();
    this.requestMethod = options.requestMethod || 'GET';
}

Service.prototype.dataToNode = function(element, parent, data){
    var toAppend = document.createElement(element);
    toAppend.innerHTML = data;
    return parent.appendChild(toAppend);
};

function Resource (options) {
    this.options = options || {};
    this.service = new Service(this.options);
}

answered Apr 21, 2014 at 20:40

Esailija

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2 Comments

agconti Over a year ago

great. I was hoping to define everything in the resource object. Is there away to accomplish that?

Esailija Over a year ago

@agconti you can move the code there but that is absurd

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