Classical Inheritance in JavaScript. Douglas Crockford www.crockford.com And you think you're so clever and classless and free — John Lennon JavaScript is a class-free, object-oriented language, and as such, it uses prototypal inheritance instead of classical inheritance. This can be puzzling to programmers trained in conventional object-oriented languages like C++ and Java. JavaScript's prototypal inheritance has more expressive power than classical inheritance, as we will see presently.
But first, why do we care about inheritance at all? The second reason is code reuse. To demonstrate this, we will introduce a little sugar which will let us write in a style that resembles a conventional classical language. Classical Inheritance First, we will make a Parenizor class that will have set and get methods for its value, and a toString method that will wrap the value in parens. The syntax is a little unusual, but it is easy to recognize the classical pattern in it. So now we can write As you would expect, myString is "(0)".
Sugar. Private Static Members in Javascript. Introduction It was a widely held belief that javascript objects could not have private instance members, that all javascript object properties where public and could be accessed and changed with external code. Douglas Crockford has demonstrated that closures can be used to provide javascript objects with private members. Douglas Crockford describes how the invocation of the constructor forms a closure that allows all of the parameters, local variables and any functions defined as function fncName(){ ... ); within the constructor to remain associated with the object that is constructed as its private members. And how inner functions assigned to properties of the object instance (with this.methodName = function(){ ... };) become "privileged" methods. Privileged because they have direct access to the private members of the object. In Java the modifiers private, public, package and protected can be combined with additional modifiers, one of which is static.
Note: General. Note: Inheritance. A JavaScript Module Pattern. Eric Miraglia (@miraglia) is an engineering manager for the YUI project at Yahoo. Eric has been at Yahoo since 2003, working on projects ranging from Yahoo Sports to YUI. For the past several years, Eric and his colleagues on the YUI team have worked to establish YUI as the foundation for Yahoo’s frontend engineering work while open-sourcing the project and sharing it with the world under a liberal BSD license. Eric is an editor and frequent contributor to YUIBlog; his personal blog is at ericmiraglia.com.
Prior to working at Yahoo, Eric taught writing at Stanford and elsewhere and led frontend engineering teams at several startups. Global variables are evil. Douglas Crockford has been teaching a useful singleton pattern for achieving this discipline, and I thought his pattern might be of interest to those of you building on top of YUI. 1. YAHOO.namespace("myProject"); This assigns an empty object myProject as a member of YAHOO (but doesn’t overwrite myProject if it already exists). 2.
Adequately Good - JavaScript Module Pattern: In-Depth - by Ben Cherry. The module pattern is a common JavaScript coding pattern. It's generally well understood, but there are a number of advanced uses that have not gotten a lot of attention. In this article, I'll review the basics and cover some truly remarkable advanced topics, including one which I think is original. The Basics We'll start out with a simple overview of the module pattern, which has been well-known since Eric Miraglia (of YUI) first blogged about it three years ago.
If you're already familiar with the module pattern, feel free to skip ahead to "Advanced Patterns". Anonymous Closures This is the fundamental construct that makes it all possible, and really is the single . (function () { // ... all vars and functions are in this scope only // still maintains access to all globals }()); Notice the () around the anonymous function. Global Import JavaScript has a feature known as . Luckily, our anonymous function provides an easy alternative. Module Export Advanced Patterns Augmentation Sub-modules. JavaScript Design Patterns: Composite | Joe Zim's JavaScript BlogJoe Zim's JavaScript Blog. My last post was about the Bridge Design Pattern, which continued the JavaScript Design Patterns series that started off with the Singleton. Today we’ve moved onto the Composite Pattern. Composites are quite useful. By definition of the word “composite”, Composites are composed of multiple parts to create one whole entity.
These are the two main benefits that the Composite pattern provides: You can treat the whole collection of objects the same way you would treat any of the individual objects in the collection. It organizes the objects into a tree structure, and since each composite object contains a method to get its children, you can hide the implementation and organize the children in any way you wish. Structure of the composite pattern In the Composite patterns hierarchy, there are two types of objects: leaf and composite. Examples of the Composite Pattern There a number of somewhat common examples of the Composite pattern. If you look around, I’m sure you’ll see some more examples. The Module Pattern, A Little More Detail - macwright.org. Once you’ve read this, read the update which has more detailed information about the module pattern’s performance profile!
This is an article on the module pattern for Javascript, and some of its neat properties when used for instances. I’ve been using it recently for projects like mapbox.js, and think it’s a neat way to structure code and avoid some of the less likable parts of the language. For those already doing Javascript: here’s why you should care. You can mostly avoid the problem of tracking the meaning of Javascript’s pesky this keyword, and the associated problem of rebinding functions to another this value.You can keep truly internal ‘states’ of your code private while exposing minimal APIs that you know will stay stable.Often this yields code that’s more friendly to Javascript compression, like I wrote about in Writing Javascript For SizeYou can avoid the sneaky problems of users forgetting the new keyword, and the workarounds people use to dodge them Let’s Begin A Quick Summary.
JavaScript Design Patterns: Singleton | Joe Zim's JavaScript BlogJoe Zim's JavaScript Blog. This is the first in what should be a pretty long series about JavaScript design patterns. In 1995, Erich Game, Richard Helm, Ralph Johnson and John Vlissides (known as the Gang of Four) published Design Patterns: Elements of Reusable Object-Oriented Software, a book cataloging recurring solutions to common dilemmas in software architecture and design. It also started a common vocabulary for referring to these solutions. If you’d like to know more you can find it on Wikipedia.
That book’s example implementations of each of the solutions were written in C++ and Smalltalk, which are quite different than JavaScript. Another book – Pro JavaScript Design Patterns – was written to bring many of those patterns into the context of JavaScript. My hope is to present a lot of the knowledge from that book here, but not so much that I get sued… just enough to keep you interested and possibly get you to buy the book. A Basic Singleton JavaScript Namespacing Page-Specific JavaScript Code About the Author.
Learning JavaScript Design Patterns. Design patterns are reusable solutions to commonly occurring problems in software design. They are both exciting and a fascinating topic to explore in any programming language. One reason for this is that they help us build upon the combined experience of many developers that came before us and ensure we structure our code in an optimized way, meeting the needs of problems we're attempting to solve. Design patterns also provide us a common vocabulary to describe solutions. This can be significantly simpler than describing syntax and semantics when we're attempting to convey a way of structuring a solution in code form to others.
In this book we will explore applying both classical and modern design patterns to the JavaScript programming language. Target Audience This book is targeted at professional developers wishing to improve their knowledge of design patterns and how they can be applied to the JavaScript programming language. Acknowledgments Credits Reading We already use patterns everyday.
JavaScript design patterns – Part 1: Singleton, composite, and façade. JavaScript design patterns – Part 2: Adapter, decorator, and factory. You have come to Part 2 of this JavaScript Design Patterns series. It's been a little while since Part 1, so you might want to refresh yourself on the singleton, composite, and façade patterns. Also, Part 3 discusses another 3 design patterns: proxy, observer, and command. This time around, you learn about the Adapter, Decorator, and Factory patterns. The adapter pattern is allows you to transform (or adapt) an interface to your needs. This is done by creating another object that has the interface you desire and connecting to the object that you're trying to change the interface of. Figure 1. Why Do You Need the Adapter? Often enough, you're working on an application and you decide that you need to replace a chunk of it, for example a library you're using for keeping logs or something of that nature.
Go through all of your code and change everything that refers to the old library.Create an adapter so that the new library can be used with the same interface as the old one. How Do You Use It?