Book Image

Node.js Design Patterns - Third Edition

By : Mario Casciaro, Luciano Mammino
5 (1)
Book Image

Node.js Design Patterns - Third Edition

5 (1)
By: Mario Casciaro, Luciano Mammino

Overview of this book

In this book, we will show you how to implement a series of best practices and design patterns to help you create efficient and robust Node.js applications with ease. We kick off by exploring the basics of Node.js, analyzing its asynchronous event driven architecture and its fundamental design patterns. We then show you how to build asynchronous control flow patterns with callbacks, promises and async/await. Next, we dive into Node.js streams, unveiling their power and showing you how to use them at their full capacity. Following streams is an analysis of different creational, structural, and behavioral design patterns that take full advantage of JavaScript and Node.js. Lastly, the book dives into more advanced concepts such as Universal JavaScript, scalability and messaging patterns to help you build enterprise-grade distributed applications. Throughout the book, you’ll see Node.js in action with the help of several real-life examples leveraging technologies such as LevelDB, Redis, RabbitMQ, ZeroMQ, and many others. They will be used to demonstrate a pattern or technique, but they will also give you a great introduction to the Node.js ecosystem and its set of solutions.
Table of Contents (16 chapters)
14
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15
Index

State

The State pattern is a specialization of the Strategy pattern where the strategy changes depending on the state of the context.

We have seen in the previous section how a strategy can be selected based on different variables such as a configuration property or an input parameter, and once this selection is done, the strategy remains unchanged for the rest of the lifespan of the context object. In the State pattern, instead, the strategy (also called the state in this circumstance) is dynamic and can change during the lifetime of the context, thus allowing its behavior to adapt depending on its internal state.

The following figure shows us a representation of the pattern:

Figure 9.2: The State pattern

Figure 9.2 shows how a context object transitions through three states (A, B, and C). With the State pattern, at each different context state, we select a different strategy. This means that the context object will adopt a different behavior based...