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This is an area where knowledge of design patterns can prove invaluable. In the first part of this book, we will explore the history and importance of design patterns which can really be applied to any programming language.

If you're already sold on or are familiar with this history, feel free to skip to the chapter "What is a Pattern. Design patterns can be traced back to the early work of an architect named Christopher Alexander. He would often write publications about his experience in solving design issues and how they related to buildings and towns. One day, it occurred to Alexander that when used time and time again, certain design constructs lead to a desired optimal effect.

In collaboration with Sara Ishikawa and Murray Silverstein, Alexander produced a pattern language that would help empower anyone wishing to design and build at any scale. This was published back in 1977 in a paper titled "A Pattern Language", which was later released as a complete hardcover book.

Some 30 years ago, software engineers began to incorporate the principles Alexander had written about into the first documentation about design patterns, which was to be a guide for novice developers looking to improve their coding skills. It's important to note that the concepts behind design patterns have actually been around in the programming industry since its inception, albeit in a less formalized form.

One of the first and arguably most iconic formal works published on design patterns in software engineering was a book in 1995 called Design Patterns: Elements Of Reusable Object-Oriented Software. This was written by Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides - a group that became known as the Gang of Four (or GoF for short). The GoF's publication is considered quite instrumental to pushing the concept of design patterns further in our field as it describes a number of development techniques and pitfalls as well as providing twenty-three core Object-Oriented design patterns frequently used around the world today.

We will be covering these patterns in more detail in the section "Categories of Design Patterns". In this book, we will take a look at a number of popular JavaScript design patterns and explore why certain patterns may be more suitable for your projects than others.

Remember that patterns can be applied not just to vanilla JavaScript (i. A pattern is a reusable solution that can be applied to commonly occurring problems in software design - in our case - in writing JavaScript web applications.

Another way of looking at patterns are as templates for how we solve problems - ones which can be used in quite a few different situations. So, why is it important to understand patterns and be familiar with them. Design patterns have three main benefits:Patterns are not an exact solution.

To understand how useful patterns can be, let's review a very simple element selection problem that the jQuery library solves for us. Imagine that we have a script where for each DOM element found on a page with class "foo" we wish to increment a counter.

What's the most efficient way to query for this collection of elements. Well, there are a few different ways this problem could be tackled: Select all of the elements in the page and then store references to them. Next, filter this collection and use regular expressions (or another means) to only store those with the class "foo". Use a modern native browser feature such as querySelectorAll() to select all of the elements with the class "foo".

Use a native feature such as getElementsByClassName() to similarly get back the desired collection. So, which of these options is the fastest. It's actually option 3. In a real-world application however, 3. Developers using jQuery don't have to worry about this problem however, as it's luckily abstracted away for us using the Facade pattern. As we'll review in more detail later, this pattern provides a simple set of abstracted interfaces (e. As we've seen, this means less time having to be concerned about implementation level details.

Behind the scenes, the library simply opts for the most optimal approach to selecting elements depending on what our current browser supports and we just consume the abstraction layer. This is significantly more easy to use for selecting HTML elements on a page versus having to manually opt for getElementById(), getElementsByClassName(), getElementsByTagName() and so on. Although we know that querySelectorAll() attempts to solve this problem, compare the effort involved in using jQuery's Facade interfaces vs.

Abstractions using patterns can offer real-world value. Remember that not every algorithm, best practice or solution represents what might be considered a complete pattern. There may be a few key ingredients here that are missing and the pattern community is generally wary of something claiming to be one unless it has been heavily vetted.

Even if something is presented to us which appears to meet the criteria for a pattern, it should not be considered one until it has undergone suitable periods of scrutiny and testing by others.

Looking back upon the work by Alexander once more, he claims that a pattern should both be a process and a "thing". This definition is obtuse on purpose as he follows by saying that it is the process which should create the "thing". This is a reason why patterns generally focus on addressing a visually identifiable structure i. In studying design patterns, it's not irregular to come across the term "proto-pattern". Well, a pattern that has not yet been known to pass the "pattern"-ity tests is usually referred to as a proto-pattern.

Proto-patterns may result from the work of someone that has established a particular solution that is worthy of sharing with the community, but may not have yet had the opportunity to have been vetted heavily due to its very young age. Alternatively, the individual(s) sharing the pattern may not have the time or interest of going through the "pattern"-ity process and might release a short description of their proto-pattern instead. Brief descriptions or snippets of this type of pattern are known as patlets.

The work involved in fully documenting a qualified pattern can be quite daunting. Looking back at some of the earliest work in the field of design patterns, a pattern may be considered "good" if it does the following: We would be forgiven for thinking that a proto-pattern which fails to meet guidelines isn't worth learning from, however, this is far from the truth. Many proto-patterns are actually quite good.

One of the additional requirements for a pattern to be valid is that they display some recurring phenomenon. This is often something that can be qualified in at least three key areas, referred to as the rule of three. To show recurrence using this rule, one must demonstrate:You may be curious about how a pattern author might approach outlining structure, implementation and purpose of a new pattern. A design pattern should have a:Design patterns are quite a powerful approach to getting all of the developers in an organization or team on the same page when creating or maintaining solutions.

If considering working on a pattern of your own, remember that although they may have a heavy initial cost in the planning and write-up phases, the value returned from that investment can be quite worth it.

Always research thoroughly before working on new patterns however, as you may find it more beneficial to use or build on top of existing proven patterns than starting afresh.