This is a simple game, written in JavaScript. The game idea was taken from book "Invent Your Own Computer Games with Python" by Albert Sweigart ( https://inventwithpython.com/chapter13.html ).
It works with javascript canvas object and is designed using an ASCII interface, found in classical roguelikes.
Use [A], [D] keys to steer the boat, [W] key to move the boat, [Z] key to place sonar device. A number on Sonar device indicates the distance to closest treasure. Drop sonar onto treasure to collect it. Once you have collected the treasure, other sonar devices will update their displayed values to show the actual distance to treasure.