Actually, i reinstalled my windows on day 1, so it was 2 days, and the grid placement system was already done in 1 day. The spawning of the phisics objects was done in day 2. long strory short: it was made in 2 days. :) (JS is awesomeee)
Yes, thanks to HTML5 <canvas> element. There are even "game engines", for JavaScript (Such as: kaboom.js, and THREE.js) I made my game using only a canvas, and HTML + CSS for the UIs. I think it is a good combo. (fast graphics, with you controlling EVERYTHING, and beautiful ui, using CSS)