Obsidian CustomJS is a powerful plugin that allows developers to extend the functionality of Obsidian, a popular note-taking app. With CustomJS, you can create custom scripts and commands, register individual commands via settings, and even assign custom hotkeys for those registered commands. The plugin also provides a state object that can be used to preserve data during modifications to the vault. Additionally, it includes a deconstructor function that can be used to perform cleanup work when the plugin is reloaded. Overall, CustomJS is an essential tool for anyone looking to customize and extend their Obsidian experience.