https://stackoverflow.com/questions/26855423/how-to-require-a-specific-string-in-typescript-interface
This was released in version 1.8 as "string literal types"
string with fixed values:
What's New in Typescript - String Literal Types
Example from the page:
interface AnimationOptions {
deltaX: number;
deltaY: number;
easing: "ease-in" | "ease-out" | "ease-in-out";
}
unknown key in object:https://stackoverflow.com/questions/47847561/typescript-type-for-object-with-unknown-keys-but-only-numeric-values
{ [key: string]: number }? Read the docs on indexable types: www.typescriptlang.org/docs/handbook/interfaces.html