library is a module in Typescript that exports a specific function called someFunction. This function is designed to be called with a string input that must be one of a defined set of values.
Within the library, the someFunction function is defined to only accept certain strings, such as "value1" or "value2". However, the interface specifying these possible values is not accessible outside of the module.
Let's look at the user code below, where someFunction is being used:
import { someFunction } from "library"
function doThing(text: string): void {
someFunction({
content: text,
})
}
When running this code, Typescript rightly throws an error stating that the type 'string' is not compatible with the type
'"value1" | "value2" | ...'The ideal solution would be to align the type of the text argument in doThing with the expected type in someFunction. However, since the type is lengthy and not publicly accessible due to the unexported interface, importing it directly isn't possible.
So, the challenge remains: how can we correctly type the text parameter without resorting to simply using any?