ImpactJS vs Defold

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.

Impact provides 2 types of collision detection; static and dynamic collisions. Both of which are easily integrated into game development.

Many plugins are available, including one called Impact++ which adds features like pathfinding and dynamic lighting.

Built-in map editor with support for tiling, collision layers, and actors.

Works with Box2d physics library, comes with all worthwhile elements for actors built in.

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.

Defold uses Lua, which is regarded as an easy to learn language by most.

Software and online dashboard are free of charge.

You can do a lot with drag and drop, but you're not limited -- the code (Lua, which is easy to learn) allows you more power than just visual editing usually gives you.

Going from idea to result is very important for the creative process.

Being crossplatform it is important to work on low end devices.

A very active and friendly community in forums.

You can download and modify the source code of the Editor and the engine for free.

You can invite friends from the dashboard and create games together.

It allows you to change scripts in a game while it is running live. Common use-cases is to tweak gameplay parameters or to perform debugging on a running game.