Here is a list of free JavaScript libraries. Of course there are thousands more, but these are a few that seem fun and promising for your projects.
Swiper (easy sliders) https://swiperjs.com/
Mapbox (custom interactive maps) https://www.mapbox.com/mapbox-gljs
Tippy (easy tooltips) https://tippyjs.bootcss.com/
Matter (2D physics engine) https://brm.io/matter-js/
Phaser (2D games) https://phaser.io/ + Tutorial w/ Catt Small
P5.js (creative coding) https://p5js.org/ + Coding Train ❤️
Three.JS (3D stuff) https://threejs.org/
D3 (custom charts & maps) https://d3js.org/
If you want to build something that seems to complex to code yourself, there is probably a library for that. Just googling js library for … would probably get you there :)