A really interesting and detailed development blog by Bryan Bibat.
"If you’ve visited an arcade in Asia, you might have seen a couple of arcade games which blatantly rip-off popular titles."
"At first glance, the game boils down to:
Enemies randomly spawn and move around the screen. Insert coin to get energy which you can spend to shoot at enemies. Killing enemies give you additional energy based on their toughness. Upon realizing how simple the game is, I decided to finally fulfill my childhood dream of programming my own arcade game. I’ve got spare time, decades of experience in programming, basic game development knowledge… it shouldn’t be that hard to pick up an HTML5 library as a web dev and build a game this simple, right?"