typescript Record accepts array, why?

Question

Can anyone explain why this compiles in typescript?
I tried some googling and looking it up in the typescript documentation but didn't find the answer.

type RecType = Record<string, any>
const arr: RecType = [1, 2, "three"] //or new Array(1, 2, 3)

console.log(arr)  // [1, 2, "three"] 
console.log(Array.isArray(arr)) // true
console.log(Object.keys(arr)) // ["0", "1", "2"] 

here's a typescript playground link with the code

Answer 1

After resting a little, coming back to the problem and looking a little deeper I think I understand it.

this is how Record is defined in typescript (from it's source code)

type Record<K extends keyof any, T> = {
    [P in K]: T;
};

an array can be assigned to this because

• keyof operator will return the array's indices as the keys (similar to how Object.keys does).
• the accessor [P in K]: T is valid for array because array["0"] is a valid way to access index 0 of the array (and so is array[0]

I hope I got it right, feel free to make corrections.