Modern web applications represent the new way to write software. Facebook, Twitter, and Wikipedia are some well-known examples of such applications. They run on servers, and users can access them with a browser via either desktop or mobile devices. We refer to these as “modern” applications because they combine a rich user interface with real-time interaction and the capability to connect with online services, among other capabilities.
Opa is a programming framework for JavaScript that enables you to easily write modern web applications that have all the aforementioned cool features. This book is a gentle introduction to Opa.
Traditionally, many different technologies and languages are involved when writing web applications. Not so with Opa! Opa is the only technology you need to know to write the code that runs on the client (in the browser) and the code that runs on the server, including database queries.
Opa natively supports the web platform, which is a set of technologies that includes HTML5 and CSS, and it automates many aspects of modern web application programming: Ajax/Comet client/server communication, event-driven and nonblocking code transformations, etc.
One of the main distinctive features of Opa is strong static typing, with type inference. This means that every application you write is checked by a program called a typechecker that automatically tracks inconsistencies in the application. Typing enables Opa programmers to debug applications quickly, and increases application safety and security.
As a final step, Opa generates standard code: JavaScript for the client side, Node.js, and MongoDB for the server side.
The philosophy of Opa is to support multiple platforms. It is possible to extend Opa to support different backends.
Working with Opa is as easy as 1, 2, 3:
- Write your application code in a text editor.
- Generate your application by invoking Opa.
- Run and/or deploy your application online.
In Installing Opa, you will learn how to install Opa and create your first application. Then you will develop two real applications with Opa: a mini-Wikipedia and a mini-Twitter.
The applications you develop with Opa are standard JavaScript projects that run both in the browser (where JavaScript is by far the most prevalent) and on the server. On the server side (also called the backend), the applications rely on two popular technologies for the runtime:
- Node.js, which allows you to execute JavaScript code on the server
- MongoDB, which is a NoSQL database server
Both technologies were chosen for their ability to scale, that is, easily add servers to handle more clients when your application becomes hugely popular.
The following typographical conventions are used in this book:
- Italic
- Indicates new terms, URLs, email addresses, filenames, and file extensions
-
Constant width - Used for program listings, as well as within paragraphs to refer to program elements such as variable or function names, databases, data types, environment variables, statements, and keywords
-
Constant width bold - Shows commands or other text that should be typed literally by the user
-
Constant width italic - Shows text that should be replaced with user-supplied values or by values determined by context
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The authors would like to thank Alok Menghrajani, who did a thorough review of the original draft of the book. Opa would never exist without the work of its contributors, including the core developers of Opa: Cédric Soulas, Frédéric Ye, Norman Scaife, and Quentin Bourgerie. Thank you for your impressive work.
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