Strategy Design Pattern in Javascript - Trifling Whims. I love the Strategy design pattern. I try to use it as much as I can. In its essence, the Strategy pattern uses delegation to decouple algorithms from the classes that use them. There are a few benefits to this. It prevents using big conditionals to decide which algorithm to use for the given type of object.
It separates concerns, thus reducing the complexity of the clients and it promotes composition over subclassing. It improves modularity and testability. To implement Strategy, there are usually two participants: The Strategy an object that encapsulates an algorithm. The Client (or Context) an object that can use any Strategy, in a plug-and-play manner. Here is how I use the Strategy pattern in Javascript, and how it is used in the wild to break libraries into small, plug-and-play packages. Strategy as a function A function provides a great way to encapsulate an algorithm and can be used as a Strategy. Let's illustrate this with an example. Strategy as a class Let's see how. Reflection. JavaScript Patterns. JavaScript: Function Invocation Patterns. JavaScript has been described as a Functional Oriented Language (this as opposed to Object Oriented Language). The reason is because functions in JavaScript do more than just separate logic into execution units, functions are first class citizens that also provide scope and the ability to create objects.
Having such a heavy reliance upon functions is both a blessing and a curse: It's a blessing because it makes the language light weight and fast (the main goal of its original development), but it is a curse because you can very easily shoot yourself in the foot if you don't know what you are doing. One concern with JavaScript functions is how different invocation patterns can produce vastly different results. This post explains the four patterns, how to use them and what to watch out for. The four invocation patterns are: Method InvocationFunction InvocationConstructor InvocationApply And Call Invocation Unfortunately, there is more than one pattern that can be used to invoke functions. JavaScript Module Pattern: In-Depth. 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 best feature of JavaScript. (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 implied globals.
Luckily, our anonymous function provides an easy alternative. Module Export. 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. List Out of Lambda. If you ignore the practical issues of computers like size, weight, cost, heat, and so on, what do you really need in a programming language? Let’s play around with this question. To understand this post you’ll need a basic understanding of how functions in Javascript work. If you can look at this code and understand what it prints, you’re good to go: var x = 10; var f = function(y) { console.log(x); console.log(y);} var g = f; f(1);g(2); This blog post is a thought exercise.
It’s not something you’d ever use for real code. I’m going to use Javascript for the examples. If you’ve already seen this kind of thing before (maybe you’ve gone through The Little Schemer or SICP) you may want to just skim the code here and look for anything new. The Little Schemer: If you haven’t seen anything like this, then you’re in for a treat! Finally: if you get stuck, don’t worry. Lists Let’s get started. Var names = ["Alice", "Bob", "Candice"]; List Out of If That’s it! Map.