Locomotive is architected to make it easy to develop web applications while encouraging the use of best practices. Locomotive is powered by high caliber Node.js modules and promotes time-tested design patterns, yielding applications that have high performance and horizontal scalability.
At the core of Locomotive is the Model View Controller design pattern, often referred to simply by its abbreviation MVC. MVC improves the architecture of an application by separating the user interface (the View) from the underlying data (the Model). Logic in the controller is used to bind the model and the view.
This separation of concerns helps to organize code, making it quicker to develop, cheaper to maintain, and easier to test.
(Aside: Design pattern enthusiasts will note that MVC, as implemented by Locomotive, is more accurately termed Model 2. Because the distinction is not widely known, this guide will continue to use MVC to refer to the pattern.)
The model represents the data used by an application, and the rules to manipulate that data. This includes loading data from a database, and validating data before storing it.
The view represents the user interface of an application. In Locomotive, views are often HTML files with embedded JavaScript. A view is rendered by the application in response to a request, at which point it is displayed to the user in a web browser.
The controller provides the glue between the model and the view. In Locomotive, controllers process incoming requests from the web browser, loading data from models and passing that data on to a view for presentation.
REST is a set of architectural principles for building distributed systems, and has emerged as the predominant model for designing web services.
The concepts were introduced by Roy T. Fielding in his doctoral thesis: Architectural Styles and the Design of Network-based Software Architectures. While there are many details that can be analyzed in depth, in terms of Locomotive the following key points apply:
Locomotive provides resource routing that makes it easy to follow REST guidelines.
For a more detailed introduction to REST, the following articles are recommended reading:
The Node.js community has embraced an aesthetic characterized by minimalistic modules and radical reusability. Locomotive follows suit, reusing existing modules while layering on only the necessary amount higher-level structure. It does this while preserving flexibility, allowing developers the freedom to chose exactly which database and template engine best suits the requirements of their application.
The Express and Connect combination has set the de facto standard for HTTP middleware in Node.js.
Locomotive builds entirely on top of Express - every Locomotive application is also an Express application. This ensures seamless compatibility with the wide variety of Connect-compatible middleware that has been developed.
Express has also set the de facto standard for pluggable template engines in Node.js.
Locomotive inherits the view layer provided by Express, again ensuring seamless compatibility with EJS, Jade, and other compliant template engines.
Locomotive does not provide a model layer of its own, recognizing that in the era of big data and real-time events, the challenges faced by modern web applications demand polyglot persistence.
Rather than being trapped behind a restrictive and limiting abstraction, developers are free to choose the database (or databases) and object mapping layer that best fits their needs.