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Asked: 2026-06-03T21:47:37+00:00

Here is my code to achieve my inheritance: <html lang=en> <head> <title>JavaScript Patterns</title> <meta

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Here is my code to achieve my inheritance:

<html lang="en">
<head>
    <title>JavaScript Patterns</title>
    <meta charset="utf-8">
</head>
<body>
    <script>
        /* Title: Classical Pattern #5 - A Temporary Constructor (a pattern that should be generally avoided)
         Description: first borrow the constructor and then also set the child's prototype to point to a new instance of the constructor
         */


        /* Basic */
        /*function inherit(C, P) {
         var F = function () {};
         F.prototype = P.prototype;
         C.prototype = new F();
         }*/


        /* Storing the Superclass */
        /*function inherit(C, P) {
         var F = function () {};
         F.prototype = P.prototype;
         C.prototype = new F();
         C.uber = P.prototype;
         }*/


        /* Resetting the Constructor Pointer */
        /*function inherit(C, P) {
         var F = function () {};
         F.prototype = P.prototype;
         C.prototype = new F();
         C.uber = P.prototype;
         C.prototype.constructor = C;
         }*/


        /* in closure */
        var inherit = (function () {
            var F = function () {
            };
            return function (C, P) {
                F.prototype = P.prototype;
                C.prototype = new F();
                C.uber = P.prototype;
                C.prototype.constructor = C;
            }
        }());


        function Parent(name) {
            this.nameParent = name || 'Adam';
            this.parentName = "parent";//this.nameParent;
        }


        // adding functionality to the prototype
        Parent.prototype.say = function () {
            return this.nameParent;
        };



        // child constructor
        function Child(nameChild) {
            console.log("parentprop:" + this.parentName);
        }

        inherit(Child, Parent);


        var kid = new Child();
        console.log(kid.name); // undefined
        console.log(typeof kid.say); // function
        kid.nameParent = 'Patrick';
        console.log(kid.parentName);
        console.log(kid.say()); // Patrick
        console.log(kid.constructor.nameParent); // Child
        console.log(kid.constructor === Parent); // false




        // reference
        // http://shop.oreilly.com/product/9780596806767.do
    </script>
</body>

I need the Child console.log to display “parent” from the parent class inherited, but for now, it only displays undefined.

I don’t know why it doesn’t inherit from parent property.

Thanks in advance for your help.

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1 Answer

  1. Editorial Team

    Because you never call the function Parent, which is what’s setting the property. If you look closely at your inherit function, you’re using the prototype property of P but you’re never calling P — which is a good thing; it’s Child who should call P:

    function Child(nameChild) {
    Parent.call(this);
    console.log("parentprop:" + this.parentName);
}

    Obviously, this has the disadvantage that you have to list Parent in more than one place — both in your call to inherit, and in Child. You could mitigate that by setting the parent constructor on the child function in inherit:

    var inherit = (function () {
    var F = function () {
    };
    return function (C, P) {
        F.prototype = P.prototype;
        C.parent = P;          // <==== The new bit
        C.prototype = new F();
        C.uber = P.prototype;
        C.prototype.constructor = C;
    }
}());

    …so then Child becomes:

    function Child(nameChild) {
    Child.parent.call(this);
    console.log("parentprop:" + this.parentName);
}

    If you’re interested in doing hierarchies thoroughly (with support for calling “super” methods and such), you might want to look at my Lineage toolkit. It’s a small toolkit that automates a lot of this stuff, but if you want to learni how this stuff works, the source might make for interesting reading. There’s also a wiki page there showing multi-layer, fully-functional inheritance without using Lineage (as a means of comparing it with using Lineage).

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