Here's some code to consider:
const obj = {
a: 1,
b: 2
}
let possibleKey: string = 'a'
if (possibleKey in obj) console.log(obj[possibleKey])
When possibleKey in obj evaluates to true, shouldn't we expect possibleKey to have the type keyof typeof obj? Why doesn't TypeScript automatically narrow down the type of string to that specific type? Instead, it throws the error message:
Element implicitly has an 'any' type because expression of type 'string' can't be used to index type '{ a: number; b: number; }'.