If you have ever wanted to build a small browser game on the side, the hardest call is usually what kind of game, not which framework. Here is how to read a genre the way you would read a spec, as a list of systems with a known build order.
A Genre Defines Done
A platformer is a game loop, a physics step for gravity and jumping, tile collision, a camera that follows the player and a level made of solid tiles. A tower defense game is a pathfinding grid, a wave spawner, turrets that target and fire, projectiles and an economy. Write that list down and the project stops being open ended. You know what finished looks like, and you can estimate it.
The Shared Parts
Most of those systems repeat across genres. The game loop is universal. Object pooling shows up the moment you have bullets or particles, so shooters, runners and tower defense all need it. A save system serves idle games, RPGs and card games alike. Collision sits under platformers, shooters and physics puzzles. That overlap is why a second game ships faster than the first, you are reusing modules, not starting over.
Start With the Smallest Spec
The idle or clicker game is the smallest real spec: a click that earns currency, generators that earn it passively, offline earnings and prestige. The interesting system is the cost curve. Each extra generator usually costs a fixed multiplier more than the last, around 15 percent, so cost = base x 1.15^owned while output climbs more gently. Tuning that curve is the whole difficulty, with no collision, physics or networking. The idle and clicker game walkthrough builds one from the first click to prestige.
Choose the Engine From the System List
For 2D genres built on sprites, tilemaps and arcade collision, Phaser ships most of those systems out of the box, and PixiJS gives you raw rendering when you want to own the architecture. For 3D, Three.js is a renderer you build on and Babylon.js is closer to a full engine. Multiplayer genres add a separate decision: WebSockets for transport and often a room server like Colyseus for authoritative state.
The Takeaway
Treat the genre as the spec, list its systems, and start with the shortest list. The guide to building each web game genre breaks down eleven genres with their systems, a recommended stack and an honest difficulty rating.