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


Opa is a functional language. One of its features is that functions are regular values, which means a function may be passed as a parameter or returned as a result. As such, they follow the same naming rules as any other value.

function f(x,y){      // function f with the two parameters x and y
  x + y + 1
function int f(x,y){  // explicitly indicates the return type
  x + y + 1

Last expression return

You may notice that there is no return inside the body of a function. That's because Opa uses last expression return, which means the last expression of a function is the return value. For example:

function max(x,y){
  if(x >= y) x else y

If x is greater than or equal to y, then x is the last expression and x will be returned; if y is greater than x, then y is the last expression and y will be returned.


Functionalities are usually regrouped into modules; for example:

module  M {
  x = 1
  y = x
  function test(){ jlog("testing") }

We can access the content of a module by...