Often while programming you have a need to pass in an object deep in the call stack. It can be a singleton or a special resource, such as a database handle, a browser for automated scraping, or just some value that you get early on and is needed in many places.
The common way this is handled is either by passing the value down the call stack - which is safe but highly cumbersome and results in signature duplication (i.e. the same parameters are written along the call stack), or a global variable is set - which is unsafe, hard to test and limits your ability to use the same code in different contexts, or to mock the value for testing.
This library leverages the NodeJS async_hooks API for a better solution - you can wrap an async function with an injector, and everything within the execution of this function and its constituents can access the value using a global getter function.
While the getter itself is global, the value it gets varies according to what was injected in this specific call stack.
So you get the flexibility of a global variable, with the locality of a value passed down a specific stack.