Question

I am working on my first JS project that involves inheritance and the prototype chain, and I am confused about why the creation of one object with specific data is affecting the data already in place on my second object.
The goal is to have a set of basic defaults in the full_params object literal in the “parent” object, and have some more specific defaults in the default_params object literal in the “child” object.
The child object specificRequest takes an array argument for its constructor function, adds those to its default_params, and then call the setOptions function of its prototype to add those to the full_params.

The problem is that when I create one specificRequest object and initialize it, it works fine, but then when I create a second specificRequest object, the full_params is already the same as
that of the first.

This is probably something very simple from a misunderstanding of how prototype works…

/////// PARENT OBJECT

function baseRequest(custom_params) {

    var key;

    this.full_params = {
        "SignatureVersion": "2",
        "Timestamp": Utilities.formatDate(new Date(), "GMT", "yyyy-MM-dd'T'HH:mm:ss'Z'")
    };

    this.custom_params = custom_params;

}


baseRequest.prototype.setOptions = function(arg_options) {
    var key;

    if (typeof arg_options === "object") this.custom_params = arg_options;

    // If an object of request options is passed, use that. Otherwise use whatever is already in the custom_params object.
    for (key in this.custom_params) {
        this.full_params[key] = this.custom_params[key];
    }

}





///////// CHILD OBJECT

function specificRequest(mySKUList) {
    var i;
    this.mySKUList = mySKUList;

    this.default_params = {
        "Action": "myAction",
        "Version": "2011-10-01"
    };

    for (i = 0; i < this.mySKUList.length; i++) {
        var temp_sku = this.mySKUList[i];
        var temp_sku_name = "SellerSKUList.SellerSKU." + (i + 1);
        this.default_params[temp_sku_name] = temp_sku;
    }

    this.setOptions(this.default_params);
}

specificRequest.prototype = new baseRequest






///// Function to run

function testfoo() {

    var skulist1 = ["AR6100", "AR6102", "WB1234"]
    var skulist2 = ["XY9999"]

    var req1 = new specificRequest(skulist1);
    var req2 = new specificRequest(skulist2);

    // Req1 has AR6100, AR6102, and WB1234 as parameters, as expected
    // Req2 should only have XY9999, but instead has XY9999, AR6102, and WB1234
}

Answer 1

Well you have tied a concrete instance of the parent class to be the prototype of the child class with this line:

specificRequest.prototype = new baseRequest

Instead, don’t instantiate the parent class at all:

specificRequest.prototype = Object.create( baseRequest.prototype );

Also, call super() equivalent when constructing a child instance:

function specificRequest(mySKUList) {
     baseRequest.call( this );

     ...
}

And please start constructor names with UpperCase.