When comparing ImpactJS vs Phaser.io, the Slant community recommends Phaser.io for most people. In the question“What are the best 2D game engines?” Phaser.io is ranked 8th while ImpactJS is ranked 57th.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Extensive documentation available to support development
ImpactJS has an active user community that busily produces tremendous resources including videos, books, tutorials, walkthroughs and more. There are also comprehensive class documentation available.
Pro Excellent collision detection system
Impact provides 2 types of collision detection; static and dynamic collisions. Both of which are easily integrated into game development.
Pro Extendable
Many plugins are available, including one called Impact++ which adds features like pathfinding and dynamic lighting.
Pro Level editor
Built-in map editor with support for tiling, collision layers, and actors.
Pro Optimized
Works with Box2d physics library, comes with all worthwhile elements for actors built in.
Pro Truly cross-platform allowing developers to build for anything
Extending the reach of a game developed with ImpactJS is easy due to the cross-platform nature the framework. There are Considerations around performance, resolution and audio, however all can be appropriately addressed when in development. Works in the browser via Canvas, even on mobile. Easily translatable into a packaged app.
Pro Great community resources
Pro Built-in Arcade Particle system
Pro WebGL and Canvas rendering modes
You can choose WebGL or classic HTML canvas element for game rendering.
Pro Very active development
This is one of the most developed frameworks right now.

Pro Good tutorials, courses and books
There are plenty of great learning resources available for Phaser.io.
Pro Super-simple loading of assets
Pro Excellent tools for sprites
Pro Support for Arcade Physics, Ninja Physics and p2.js
Pro Easy to learn
Most tasks are done just using 2 or 3 lines of code.


Pro Very fast to develop with
If you're browsing Slant, you probably already have a JavaScript enabled browser, which is most of what you need to get started learning JavaScript. The requirement to run a server locally on your computer while developing might make things a little more difficult
Pro No install required
All you need to do is attach Phaser script to a HTML page even without installing any extensions.
Pro Easy to understand if you have used flash
Phaser provides a similar approach as to that of Flash games, where you can load assets and place them on a stage, and even improves upon the shortcomings of actionscript. It is very easy to shift from flash to HTML5 development because of this approach.
Pro You can run it in the cloud
You can use it in popular online editors like replit, codandbox, etc.
Pro Animating is easy
Pro Has separate versions maintained by developer and the community
The creator of phaser(photonstorm) has given the older(Phaser 2.0) source code to the community for their own maintenance, and has made Phaser 3.0 with a different style and approach, trying to make it easier for beginners to learn.
Cons
Con Inactive
The last update was in 2014.
Con Cost of $99
While most HTML5 frameworks are offered as free open source projects, ImpactJS has a one time cost and no free option.
Con Using Cordova to Export for Mobile
To export to mobile games you need to use cordova.
Con Official documentation is not so good

Con Poor performance
As long as your map is not larger than 600*400px, everything is fine.
Con Extremely many bugs
Con Developer ignores community needs
