Upgrading from AngularJS to Angular

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Upgrading from AngularJS to Angular

Angular is the name for the Angular of today and tomorrow. AngularJS is the name for all 1.x versions of Angular.

AngularJS apps are great. Always consider the business case before moving to Angular. An important part of that case is the time and effort to get there. This guide describes the built-in tools for efficiently migrating AngularJS projects over to the Angular platform, a piece at a time.

Some applications will be easier to upgrade than others, and there are many ways to make it easier for yourself. It is possible to prepare and align AngularJS applications with Angular even before beginning the upgrade process. These preparation steps are all about making the code more decoupled, more maintainable, and better aligned with modern development tools. That means in addition to making the upgrade easier, you will also improve the existing AngularJS applications.

One of the keys to a successful upgrade is to do it incrementally, by running the two frameworks side by side in the same application, and porting AngularJS components to Angular one by one. This makes it possible to upgrade even large and complex applications without disrupting other business, because the work can be done collaboratively and spread over a period of time. The upgrade module in Angular has been designed to make incremental upgrading seamless.


There are many ways to structure AngularJS applications. When you begin to upgrade these applications to Angular, some will turn out to be much more easy to work with than others. There are a few key techniques and patterns that you can apply to future proof apps even before you begin the migration.

Follow the AngularJS Style Guide

The AngularJS Style Guide collects patterns and practices that have been proven to result in cleaner and more maintainable AngularJS applications. It contains a wealth of information about how to write and organize AngularJS code - and equally importantly - how not to write and organize AngularJS code.

Angular is a reimagined version of the best parts of AngularJS. In that sense, its goals are the same as the AngularJS Style Guide's: To preserve the good parts of AngularJS, and to avoid the bad parts. There's a lot more to Angular than just that of course, but this does mean that following the style guide helps make your AngularJS app more closely aligned with Angular.

There are a few rules in particular that will make it much easier to do an incremental upgrade using the Angular upgrade/static module:

  • The Rule of 1 states that there should be one component per file. This not only makes components easy to navigate and find, but will also allow us to migrate them between languages and frameworks one at a time. In this example application, each controller, component, service, and filter is in its own source file.
  • The Folders-by-Feature Structure and Modularity rules define similar principles on a higher level of abstraction: Different parts of the application should reside in different directories and NgModules.

When an application is laid out feature per feature in this way, it can also be migrated one feature at a time. For applications that don't already look like this, applying the rules in the AngularJS style guide is a highly recommended preparation step. And this is not just for the sake of the upgrade - it is just solid advice in general!

Using a Module Loader

When you break application code down into one component per file, you often end up with a project structure with a large number of relatively small files. This is a much neater way to organize things than a small number of large files, but it doesn't work that well if you have to load all those files to the HTML page with