TypeScript widens the type of x to allow `number | string`, there are no type errors below:
const x = []
x.push(1)
type t = typeof x
// ^? type t = number[]
x[0] = "new"
type t2 = typeof x
// ^? type t2 = (number | string)[]
const y = x[0] + "oops"
// ^? const y: string