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