Javascript 2DRaycast help

Hi there, I'm working on a simple stealth game in unity2D, the very core gameplay will involve hiding from enemy sight as they look around. I'm relatively new to scripting and I've tried to find tutorials on how I'd do this, however the majority were in c#.

Basically I'd like a 2d raycast from an enemy that faces down, and switches between 2 positions. If the player walks into it, there's an event that's triggered. However there''s a crate between two of these points, and if the player is in front of the crate, the enemy is not alerted.

I hope this makes sense, and I appreciate all the help. :)