You can use the dialog enum values as keys, but they need to be computed properties:
let openDialogs: { [key in DialogType]?: Dialog } = {
[DialogType.Options]: undefined,
};
When referencing an enum constant with an expression, you use a String literal. For example, consider this Enum class:
public enum Suit {hearts, spades, diamonds, clubs}
To refer to the Suit constant, Suit.hearts with an expression, you use the String literal, "hearts"