[Typescript] “Record” Mapped Type

type MyRecord<K extend string, T> = {
   [P in K]: T       
}

array[0]

array[0] 
array["0"]

let dictionary: Record<string, TrackStates> = {}

interface TrackStates {
    current: string;
    next: string;
}

const item: Record<keyof TrackStates, string> = {
    current: ‘abc‘,
    next: ‘‘def
}

dictionary[0] = item