jQuery plugins have few concrete rules, which is one of the reasons for the incredible diversity in how they are implemented across the community. This effectively could be used to break down an application into smaller, more loosely coupled blocks to improve code management and potentials for re-use. It's possible to lazy load scripts if this is needed. In studying design patterns, it's not irregular to come across the term "proto-pattern". There are some interesting points worth noting about Smalltalk-80's MVC architecture: Developers are sometimes surprised when they learn that the Observer pattern (nowadays commonly implemented as the Publish/Subscribe variation) was included as a part of MVC's architecture many decades ago. that an AMD loader must account for, and so jQuery only registers with This gets automatically assigned to basketModule so that we can interact with it as follows: The methods above are effectively namespaced inside basketModule. 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. The benefit of this architecture is that each component plays its own separate role in making the application function as needed. Views expose setters which presenters can use to set data. Let us qualify the reason behind this. In the next sample, we demonstrate a number of different ways in which we can check to see if a variable (object or plugin namespace) already exists, defining it if it doesn't. Below we can see some examples of this: For those wishing to use the Publish/Subscribe pattern with vanilla JavaScript (or another library) AmplifyJS includes a clean, library-agnostic implementation that can be used with any library or toolkit. It's important to understand what the original MVC pattern was aiming to solve as it's mutated quite heavily since the days of its origin. In this chapter, we explored several time-saving design patterns and best practices that can be employed to improve how jQuery plugins can be written. The implementation for this can be found below and as we're consolidating data for multiple possible objects into a more central singular structure, it is technically also a Flyweight. Should you wish to learn more about the language, I am happy to recommend the following titles: One of the most important aspects of writing maintainable code is being able to notice the recurring themes in that code and optimize them. Developers doing so have fallen prey to inperformantly iterating through their data, wrapping it in nested divs and using outdated techniques such as document.write to inject the "template" into the DOM. Complete tutorials on these tools are outside the scope of this book, but I can recommend reading John Hann's article about curl.js and James Burke's RequireJS API documentation for more. So that we are able to get an appreciation for how many of the vanilla JavaScript implementations of the Observer pattern might work, let's take a walk through of a minimalist version of Publish/Subscribe I released on GitHub under a project called pubsubz. If we were constructing a simple Todo application, a KnockoutJS Model representing a single Todo item could look as follows: Note: One may notice in the above snippet that we are calling the method observable() on the KnockoutJS namespace ko. They consistently include an execution operation (such as run() or execute()). Not only is the pattern an easy way to implement inheritance, but it can also come with a performance boost as well: when defining a function in an object, they're all created by reference (so all child objects point to the same function) instead of creating their own individual copies. That’s right, after this you’ll no longer have any clue what post will be coming out every Monday! In our sample application using the above Observer components, we now define: We then define ConcreteSubject and ConcreteObserver handlers for both adding new observers to the page and implementing the updating interface. In JavaScript, because both variables and functions explicitly defined within such a context may only be accessed inside of it, function invocation provides an easy means to achieving privacy. The mediator extracts the workflow from the implementation details and creates a more natural abstraction at a higher level, showing us at a much faster glance what that workflow is. We can see this demonstrated in the example below: Object.create also allows us to easily implement advanced concepts such as differential inheritance where objects are able to directly inherit from other objects. In this section, we're going to review three very important architectural patterns - MVC (Model-View-Controller), MVP (Model-View-Presenter) and MVVM (Model-View-ViewModel). In Harmony, classes have been proposed for the language along with constructors and (finally) some sense of true privacy. Singletons differ from static classes (or objects) as we can delay their initialization, generally because they require some information that may not be available during initialization time. This jQuery UI Widget Factory pattern covers almost all of the supported default factory methods, including triggering events. Document the API and how the plugin is to be used. Interestingly, with the Almond AMD shim, RequireJS doesn't need to be rolled in the deployed site and what one might consider a script loader can be easily shifted outside of development. Provides a clear proposal for how to approach defining flexible modules. Based on the concept of creating an object. In practice, Flyweight data sharing can involve taking several similar objects or data constructs used by a number of objects and placing this data into a single external object. In JavaScript framework terms, this is most commonly seen in Backbone’s Collection and Model, where all Model events are bubbled up to and through its parent Collection. The idea was that decoupling these parts of the application would also allow the reuse of models for other interfaces in the application. For the purists among us, you’ll be happy to know that we can now also greatly reduce how reliant we are on data-bindings thanks to a feature known as custom binding providers, introduced in KnockoutJS 1.3 and available in all versions since. In Sexton’s article on this topic, he implemented a bridge that enables us to attach our general logic to a particular plugin, which we’ve implemented in the pattern below. The original table was summarized by Elyse Nielsen back in 2004 Models may trigger events but it's the presenters role to subscribe to them so that it can update the view. It changes Model information into View information, passing commands from the View to the Model. Whilst this book is targeted at both beginners and intermediate developers, a basic understanding of JavaScript fundamentals is assumed. The benefit this pattern offers is easy application of functional behaviour to multiple objects or namespaces and can come in useful when applying a set of base methods to be built on later (e.g. We also can't access private members in methods that are added to the object at a later point. It has long been considered (and proven) a performance bad practice to manually create large blocks of HTML markup in-memory through string concatenation. As there's been quite a lot of information presented in this section so far, let's try to bring it all together in a single example that will hopefully highlight what we have learned. Some developers feel that injecting functionality into an object prototype is a bad idea as it leads to both prototype pollution and a level of uncertainty regarding the origin of our functions. There are then four ways in which keys and values can then be assigned to an object: As we will see a little later in the book, these methods can even be used for inheritance, as follows: As we saw earlier, JavaScript doesn't support the concept of classes but it does support special constructor functions that work with objects. There should be no comma used after the final name/value pair in the object as this may result in errors. One can also opt for adding properties directly to the namespace: Object literals have the advantage of not polluting the global namespace but assist in organizing code and parameters logically. The following is an example that builds upon our previous snippets using the Constructor pattern logic to define cars. In KnockoutJS, if we wish to detect and respond to changes on a single object, we would use observables. He has also written books like Learning JavaScript Design Patterns with O'Reilly. For this, let's take a look at a sample controller from Spine.js: In this example, we're going to have a controller called PhotosController which will be in charge of individual photos in the application. The Module pattern encapsulates "privacy", state and organization using closures. The Controllers role in this pair was handling user interaction (such as key-presses and actions e.g. They're often an indication that modules in a system are either tightly coupled or that logic is overly spread across multiple parts of a codebase. Now of course, we have to keep in mind that jQuery (and Sizzle - its selector engine) are doing a lot more behind the scenes to optimize our query (and that a jQuery object, not just a DOM node is returned). This could either be a controller route (such as a Backbone.Router, covered later in the book) or a callback in response to data being fetched. addItem(), getItemCount() etc). Option 5 is a little similar to Option 4, but is a long-form which evaluates whether myApplication is undefined inline such that it's defined as an object if not, otherwise set to an existing value for myApplication if so. We can leverage this fact to promote function re-use. The mediator only uses events because it makes life easy when dealing with modern JavaScript webapp frameworks. And even if the implementations both use some of the same core constructs, I believe there is a distinct difference between them. One of the key features that landed in jQuery 1.7 was support for registering jQuery as an asynchronous module. Although implementation specific to KnockoutJS, the
containing the "You have a really long name!" There are however drawbacks that we should be aware of when implementing the pattern. The form is the solution to the problem; the context defines the problem”. 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. When a photo entry gets updated, we re-render the view to reflect the changes to the meta-data. There are two ways in which the Flyweight pattern can be applied. Well, a pattern that has not yet been known to pass the "pattern"-ity tests is usually referred to as a proto-pattern. In ES5, JavaScript is a class-less language, however classes can be simulated using functions. A template *might* be a declarative way to specify part or even all of a view object so that it can be generated from the template specification. Defining AMD-compatible modules using Dojo is fairly straight-forward. If you're already sold on or are familiar with this history, feel free to skip to the chapter "What is a Pattern?" To demonstrate the structure of this version of the Decorator pattern, we're going to imagine we have a superclass that models a Macbook once again and a store that allows us to "decorate" our Macbook with a number of enhancements for an additional fee. When two objects have a direct relationship already – say, a parent view and child view – there may be benefit in using an event aggregator. Just select your click then download button, and complete an offer to start downloading the ebook. Read 36 reviews from the world's largest community for readers. It acts as a central hub for events to pass through. Presentation was taken care of by the View, but there wasn't just a single View and Controller - a View-Controller pair was required for each section or element being displayed on the screen. Decorators are a structural design pattern that aim to promote code re-use. By simply prefixing a call to a constructor function with the keyword "new", we can tell JavaScript we would like the function to behave like a constructor and instantiate a new object with the members defined by that function. Most structural JavaScript frameworks will adopt their own take on classical patterns, either intentionally or by accident, but the important thing is that they help us develop applications which are organized, clean and can be easily maintained. We're now going to explore a minor augmentation to the nested namespacing pattern which we'll refer to as the Dependency Declaration pattern. Explore structure and semantics - this can be done by examining the interactions and context of the patterns you are interested in so you can identify the principles that assist in organizing those patterns together in useful configurations. Additionally, most of articles about JavaScript Design patterns are simply rephrasing the sentences from Learning JavaScript Design Patterns.

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