`customElements.define()`に渡す`name`のtype checkをしたかった

CustomElementName.ts

type Spread<T extends string> = T extends `${infer L}${infer R}`
  ? [L, ...Spread<R>]
  : [];

type UpperAlphabet = Spread<"ABCDEFGHIJKLMNOPQRSTUVWXYZ">[number];
type LowerAlphabet = Lowercase<UpperAlphabet>;

type SpreadCheck<T extends string, U extends string> =
  T extends `${infer L}${infer R}`
    ? L extends U
      ? [L, ...SpreadCheck<R, U>]
      : never
    : [];

type Every<T extends string, U extends string> =
  Spread<T> extends SpreadCheck<T, U>
    ? T
    : never;

type CustomElementName<T extends string> = `${string}-${string}` & Every<T, LowerAlphabet | "-">;

const defineCustomElement = <T extends string>(
  name: CustomElementName<T>,
  options?: Parameters<typeof customElements.define>[2]
) => {
  return (constructor: Parameters<typeof customElements.define>[1]) => {
    customElements.define(name, constructor, options);
  };
};

@defineCustomElement("Custom-Element-Demo!")
class Bad extends HTMLElement {}
// Argument of type 'string' is not assignable to parameter of type 'never'.

@defineCustomElement("custom-element-demo")
class Good extends HTMLElement {}
// :)