Wednesday JavaScript Meanderings

On JavaScript Parasitic Inheritance

Hmmm…. Not sure that I really buy into all the craze in Parasitic Inheritance the last couple of years. Perhaps I’d buy into it if I heard a really great technical explanation, but thus far, all I’ve heard and read about the virtues of Parasitic Inheritance center around not having to use “this” and “new.” My reaction to that line of reasoning is “So what?” “this” and “new” are artifacts of the JavaScript language. Deal with it. Another line of reasoning used to justify the use of Parasitic Inheritance is the concept of the durable object, which is defined as “A durable object contains no visible data members, and its methods use neither this nor that. Again we return to the non-use of “this.” And again, “So what?” You can achieve something similar this using while defining a custom object in the traditional way:

function myObj() {}

myObj.prototype = (function() {
    function myPrivFunction(myArg) {
       return something with myArg...
    return {
        myMethod : function(param) {
            return myPrivFunction(param);

You can have a whole set of private functions defined above the return that will not be changeable to the outside world. Furthermore, one of my biggest problems with Parasitic Inheritance is that you lose instanceof. Yes, there are ways to deal with it, but most of the examples I’ve seen deal with overriding Object and Function prototypes, or creating some intermediary “helper” function to enable instanceof with Parasitic Inheritance. My thought about this is if you have to make changes to the core of the language, then the “solution” you’re providing is simply an interesting engineering exercise.

On MVC: Put the DOM in Its Place, Dammit!

One of the things I see quite a bit of when working with JavaScript developers who are relatively new to using MVC frameworks such as Backbone.js is that their thinking is very DOM-focused. And while MVC in JavaScript does mean interaction with the DOM through the View, most developers focus their thinking around the View. As a result, their programming is all about direct references. But MVC is about separation of concerns, and each part of the MVC has an important role to play. As such, one of things that I do my best to help “teach” is having developers divorce themselves from DOM-based thinking, and start thinking at a much higher level; specifically, the system or application; breaking the application or system into constituent MVC parts.

Admittedly, it’s difficult for many to make the conceptual leap into MVC thinking because what we as UI Engineers produce ultimately shows up on the DOM. But the DOM is a by-product of MVC interaction. Once you get that concept down, then thinking with a perspective of MVC becomes quite easy.

It doesn’t help matters much when you have examples that are very DOM-focused, as many developers that move over to MVC are expert in jQuery or YUI or prototype.js, what have you. As a result, these developers provide examples that lean heavily on that previous experience. It’s a bit of vicious cycle.


1 thought on “Wednesday JavaScript Meanderings

  1. Pingback: On Classical Inheritance in JavaScript « Welcome to my dawg house!

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