Branded types are cool

Instead of doing:

type Theme = {
	primary: string;
	secondary: string;
}
 
// Hope people use the theme color strings here!
function draw(color: string) {}

You can do:

declare const themeColorBrand: unique symbol;
type ThemeColor = string & { [themeColorBrand]: never }
 
type Theme = {
	primary: ThemeColor;
	secondary: ThemeColor;
}
 
// Now you have to pass a branded color in from your theme instead
function draw(color: ThemeColor) {}

Oh this version is cool too, using a generic value:

type Currency<T> = number & { __currency: T };
 
type Euro = Currency<"euro">;
type USD = Currency<"usd">;

You could use a symbol instead of __asdf if you want too, I think

type currencyBrand: unique symbol;
type Currency<T> = number & { [currencyBrand]: T };
 
type Euro = Currency<"euro">;
type USD = Currency<"usd">;

Not sure the value of one over the other really. I think the symbol “technically” means no one can conflict with it, but like will someone really conflict __currency in practice either? And maybe it reads more clearly?