Book Image

Opa Application Development

By : Li Wenbo
Book Image

Opa Application Development

By: Li Wenbo

Overview of this book

Opa is a full-stack Open Source web development framework for JavaScript that lets you write secure and scalable web applications. It generates standard Node.js/MongoDB applications, natively supports HTML5 and CSS and automates many aspects of modern web application programming. It handles all aspects of web programming written in one consistent language and compiled to web standards.Opa Application Development is a practical,hands-on guide that provides you with a number of step-by-step exercises. It covers almost all aspects of developing a web application with Opa, which will help you take advantage of the real power of Opa, as well as building a secure, powerful web application rapidly.Opa Application Development dives into all concepts and components required to build a web application with Opa. The first half of this book shows you all of the basic building blocks that you will need to develop an Opa application, including the syntax of Opa, web development aspects, client and server communication and slicing, plugin, database, and so on. By the end of the book you will have yourself created a complete web application along with a game: Pacman!
Table of Contents (18 chapters)
Opa Application Development
About the Author
About the Reviewers

Building application logic

A chat application is all about exchanging messages between users, so we need to define a message type. We can find its definition in the first line of model.opa:

type message = {string user, string text}

It's a very simple type with two fields. The user field represents the author of the message, and the text field represents the content of the message.

Now that we have the definition of a message, we need a way to pass the messages between different clients. As mentioned in Chapter 5, Communicating between Client and Server, Opa provides three ways for communicating between clients and servers: session, cell, and network. Session is for one-way asynchronous communication; cell is a special case of session and is for two-way synchronous communication; and network is for broadcasting messages to all observers. Network is the right choice for our purpose:

server private room = Network.empty();

This code fragment defines an empty network named...