The technologies that enable the Internet tend to change, progress and evolve at rapid speeds, as requirements change and developers build better versions of the software. Angular is a case in point, with wide changes in just a few years. Google developed AngularJS in 2009 and version 1.0 was released in 2012. Angular has since dominated the world of open-source JavaScript frameworks, with enthusiastic support and widespread adoption among both enterprises and individuals. As a result, Angular has evolved from the AngularJS version 1.0 to Angular version 2.0 and now the latest Angular version 4.0, all in just five years.

Despite the potential benefits of the upgrades, some in the Angular community have concerns about migrating to a newer version. Keep reading to find out what has changed in Angular and why migrating to the latest version is a good idea. We’ll give you an in-depth comparison so you can understand the differences and make an informed decision.  

Understanding the Different Versions of Angular

Before we dive into the differences, let’s first clarify each version with a description:

• AngularJS is an open-source, JavaScript-based, front-end web application framework for dynamic web app development. It utilizes HTML as a template language. By extending HTML attributes with directives and binding data to HTML with expressions, AngularJS creates an environment that is readable, extraordinarily expressive and quick to develop. 
• Angular is the blanket term used to refer to Angular 2, Angular 4 and all other versions that come after AngularJS. Both Angular 2 and 4 are open-source, TypeScript-based front-end web application platforms. 
• Angular 4 is the latest version of Angular. Although Angular 2 was a complete rewrite of AngularJS, there are no major differences between Angular 2 and Angular 4. Angular 4 is only an improvement and is backward compatible with Angular 2. 

How Are They Different?

Below is a comparison of AngularJS to Angular, because Angular includes both version 2 and version 4. We compare architecture, language, expression syntax, mobile support, and routing. 

1. Architecture

AngularJS

The architecture of AngularJS is based on model-view-controller (MVC) design. The model is the central component that expresses the application's behavior and manages its data, logic, and rules. The view generates an output based on the information in the model. The controller accepts input, converts it into commands and sends the commands to the model and the view. 

Angular 

In Angular 2, controllers and $scope were replaced by components and directives. Components are directives with a template. They deal with a view of the application and logic on the page. There are two kinds of directives in Angular 2. These are structural directives that alter the layout of the DOM by removing and replacing its elements, and attributive directives that change the behavior or appearance of a DOM element.

In Angular 4, the structural derivatives ngIf and ngFor have been improved, and you can use if/else design syntax in your templates.   

2. Language

AngularJS

AngularJS is written in JavaScript. 

Angular

Angular uses Microsoft’s TypeScript language, which is a superset of ECMAScript 6 (ES6). This has the combined advantages of the TypeScript features, like type declarations, and the benefits of ES6, like iterators and lambdas.

Angular 4 is compatible with the most recent versions of TypeScript that have powerful type checking and object-oriented features. 

3. Expression Syntax

AngularJS

To bind an image/property or an event with AngularJS, you have to remember the right ng directive.

Angular

Angular focuses on “( )” for event binding and “[ ]” for property binding.

4. Mobile Support

AngularJS was not built with mobile support in mind, but Angular 2 and 4 both feature mobile support.

5. Routing

AngularJS uses $routeprovider.when() to configure routing while Angular uses @RouteConfig{(…)}. 

Performance 

AngularJS was originally developed for designers, not developers. Although there were a few evolutionary improvements in its design, they were not enough to fulfill developer requirements. The later versions, Angular 2 and Angular 4, have been upgraded to provide an overall improvement in performance, especially in speed and dependency injection. 

1. Speed

By providing features like 2-way binding, AngularJS reduced the development effort and time. However, by creating more processing on the client side, page load was taking considerable time. Angular2 provides a better structure to more easily create and maintain big applications and a better change detection mechanism. Angular 4 is the fastest version yet. 

2. Dependency injection

Angular implements unidirectional tree-based change detection and uses Hierarchical Dependency Injection system. This significantly boosts performance for the framework.  

Advantages and Disadvantages 

Because they are Google products, all Angular versions are trustworthy and enjoy great support from Google engineers and the large community of Angular users and developers. However, each version has its own advantages and disadvantages. 

1. AngularJS

Advantages

• It is unit testing ready.
• It has great MVC data binding makes app development fast.
• Using HTML as a declarative language makes it very intuitive.
• It is a comprehensive solution for rapid front-end development since it does not need any other frameworks or plugins.
• AngularJS apps can run on every significant program and advanced cells including iOS and Android-based phones and tablets.

Disadvantages

• It is big and complicated due to the multiple ways of doing the same thing.
• Implementations scale poorly.
• If a user of an AngularJS application disables JavaScript, nothing but the basic page is visible.
• There’s a lagging UI if there are more than 200 watchers.

2. Angular 2

Advantages

• TypeScript allows code optimization using the OOPS concept.
• It is mobile-oriented.
• It has improved dependency injection and modularity.
• It provides more choice for languages such as Dart, TypeScript, ES5, and ES6 for writing codes.
• It offers simpler routing.

Disadvantages

• It is more complicated to set up compared to AngularJS.
• It’s inefficient if you only need to create simple, small web apps. 

3. Angular 4

Advantages

• It enables a fast development process.
• It’s ideal for single-page web applications with an extended interface.
• Full TypeScript support helps in building bulky applications.
• Tests are easy to write.
• An improved View Engine generates less code in AOT mode.
• It has a modularized animation package.

Disadvantages

• It’s slow when displaying enormous amounts of data.

Conclusion

Obviously, AngularJS is still useful or else everyone would have migrated to Angular 2 or 4 by now. Each version of Angular has significant benefits, but there is much to gain in being up-to-date with the latest version. Angular is decidedly faster than AngularJS, has a mobile-driven approach,  executes better with components, and enables smoother migration from earlier versions. If you are comfortable with one version of Angular, switching to another should be easy for you—and well worth the effort.