Treating Javascript as a first-class language

With the emergence of the Single Page Application (SPA) architecture as an approach to creating more fluid and responsive user experiences in the browser, Javascript is gaining prominence as a platform for modern application development. Paypal, a large online payment service, announced recently that it has achieved significant performance and productivity gains by shifting its server-side development from Java to Javascript. From a software architecture and development perspective, what do expressions like "Javascript as a first-class language" or "Javascript as a platform" actually mean?

Let's consider a well-established first-class language and platform like Java. By the way, I still consider Java a strong and safe bet for developing applications. What makes Java strong is not just the language, but the rich ecosystem of free and open source tools and frameworks built around it (e.g., Eclipse, Tomcat, JBoss Application Server, Drools, Maven, Jenkins, Solr, Hibernate, Spring, Hadoop to name just a few). The JVM is evolving with new languages and frameworks like Groovy, Grails, Clojure, Scala, Akka, and the Play Framework which aim to enhance developer's productivity. It is also well-known that big internet companies like Twitter have achieved significant gains in performance, scalability, and other architectural concerns by shifting a lot of back-end code from Ruby on Rails to the JVM. There are a number of architectural patterns and software development practices that have been adopted over the years in successfully building quality Java applications. These include:

• Design patterns such as the Gang of Four (GoF), Dependency Injection, Model View Controller (MVC), Enterprise Integration Patterns (EIP), Domain Driven Design (DDD), and modularity patterns like those based on OSGi.
• Test-Driven Development (TDD) using tools like JUnit, TestNG, Mockito (mocking), Cucumber-JVM (for behavior-driven development or BDD), and Selenium (for automated end-to-end testing).
• Build tools like Maven and Gradle.
• Static analysis with tools like FindBugs, Checkstyle, PMD, and Sonar.
• Continuous integration and delivery with tools like Jenkins.
• Performance testing with JMeter.
• Web application vulnerability testing with Burp.

As we move to a rich client application paradigm based on Javascript and the Single Page Application (SPA) architecture, it is clear that Javascript can no longer be considered a toy language for front-end developers and so we need to bring the same engineering discipline to Javascript. As I said previously, the JVM remains my platform of choice for back-end development. For example, I find that AngularJS (a client-side Javascript MVC framework) works well with Spring back-end capabilities (like Spring Security and REST support in Spring MVC, HATEOAS, or Grail). However, I also keep an eye on server-side Javascript frameworks like Node.js.

The good news is that the community is coming up with patterns, tools, and practices that are helping elevate Javascript to the status of first-class language. The following is a list of patterns and tools that I find interesting and promising so far:

• Javascript design patterns including the application of the GoFs to Javascript. The MVC and Dependency Injection patterns are both implemented in AngularJS, my favorite Javascript MVC framework. There are also modularity patterns like Asyncronous Module Definition (AMD) supported by RequireJS.
• Functional programming support in Javascript (e.g., higher-order functions and closures) is emerging as a best practice in writing quality Javascript code. 
• Behavior-Driven Development (BDD) testing with Jasmine.
• Static analysis with Javascript code quality tools like JSLint and JSHint.
• Build with Grunt, a Javascript task runner.
• Karma, a test runner for Javascript.
• Protractor, an end-to-end test framework built on top of Selenium WedDriverJS.
• Single Page Applications are subject to common web application vulnerabilities like Cookie Snooping, Cross-Site Scripting (XSS), Cross-Site Request Forgery (CSRF), and JSON Injection. Security is mainly the responsibility of the server, although client-side frameworks like AngularJS also provide some features to enhance the security of Single Page Applications.