Library of Isaac is a universal library full of any tool you could think of needed for modding, functioning as the complete API this game was missing. The library is community contributable, basically acting as a built in version of #resources in The Modding of Isaac server. All the information needed is able to be accessed through docs.
Most of the code here was taken from isaacscript-common, a bigger and more complete Isaac library that you should check out if you want a more type-safe solution.
The library is made easily lightweight through the ability to embed code with an extension in Virtual Studio Code. With the extension, you can autofill functions, callbacks, and variables from library, automatically putting only the code necessary in its own file. Doing this makes it so the entire library doesn't have to be put into the mod for it to function, saving resources.
We also plan to make the library available as a mod for larger mods that will use a lot of the library to minimize the amount of reused code.
VSCode extension:
https://marketplace.visualstudio.com/items?itemName=ThiccoCatto.library-of-isaac-dev-extension
Documentation for the library: a