WebGL build at https://jhocking.itch.io/astar-pathfinding

Here's a library for and demo of A* on a 2D grid. Many years ago I had programmed a pathfinding library in AS3 to use in Flash, and I decided to port it to C# for use in Unity. Click and drag the green and red squares in the interactive demo to see the pathfinding algorithm in action.

For many games (especially 3D games) you would be better off using the NavMesh pathfinding built into Unity, or you could use the A* Pathfinding Project. However those approaches aren't great choices for a simple 2D grid, plus this library is a good reference for you to learn how A* works.

I relied heavily on this tutorial when I was learning the algorithm:
https://gist.github.com/jcward/45afd22560939aaae5c75e68f1e57505

Unless it's set to WebGL (because threads don't work on that platform), the demo executes the pathfinding process on a separate thread, and wraps the threaded execution in a coroutine. The wrapper has two purposes: so that Unity will keep going while the process runs, and to return the pathfinding result back to the main thread. This library doesn't have to be used on new threads, but running pathfinding on separate threads helps your game's performance when there is lots of pathfinding going on.