Differences between Promise and Observable in Angular

Code examples and video tutorials about Promise and Observable in Angular.js
05 September 2017   64706


Promise handles a single event when an async operation completes or fails.

Note: There are Promise libraries out there that support cancellation, but ES6 Promise doesn't so far.


An Observable is like a Stream (in many languages) and allows to pass zero or more events where the callback is called for each event.

Often Observable is preferred over Promise because it provides the features of Promise and more. With Observable it doesn't matter if you want to handle 0, 1, or multiple events. You can utilize the same API in each case.

Observable also has the advantage over Promise to be cancelable. If the result of an HTTP request to a server or some other expensive async operation isn't needed anymore, the Subscription of an Observable allows to cancel the subscription, while a Promise will eventually call the success or failed callback even when you don't need the notification or the result it provides anymore.

Observable provides operators like mapforEachreduce, ... similar to an array

There are also powerful operators like retry(), or replay().

AngularJS to Angular Migration Tools to be Released

New tools are called ngMigration Assistant and ngMigration Forum
17 August 2018   4054

The JS-development team AngularJS has released two customers' "helper" - ngMigration Assistant and Forum. The tools show which migration from AngularJS to Angular is correct, how to simplify the process as much as possible and avoid mistakes.

ngMigration Assistant is a command-line tool that analyzes any AngularJS application, regardless of size, and recommends an optimal migration path. It provides statistics on the complexity, size, and patterns of an app. Based on this data, the program offers a list of clear recommendations that simplify the transition from AngularJS to Angular, taking into account the size and complexity of the code.

You can find an example of using the ngMigration Assistant for the AngularJS phone catalog application below. Using the ngma command, registered in the directory, analysis is performed and recommendations are written.

Displaying ngMigration Assitant statistics
Displaying ngMigration Assitant statistics

Initially, the tool shows statistics of the available data, and after - the stages of preparation for migration to Angular.

NgMigration Assitant Recommendations
NgMigration Assitant Recommendations

The new ngMigration Forum collects up-to-date information on migration paths and tools that provide the transition from AngularJS to Angular. ngMigration Forum is a place for sharing experiences, solving problems and asking questions.

The last update of Angular 6.1 was released in late July 2018. In Angular, support for TypeScript 2.8 and 2.9 was added, as well as the ability to configure the router to store and restore the scrolling position