Helper to make class instance callable

toCallable.ts

type hasCallMethod = { call: (...args: any[]) => any };

export default function toCallable<T extends hasCallMethod>(instance: T) {
  type argsType = Parameters<T["call"]>
  const fn = (...args: argsType) => {
    return instance.call(...args);
  };

  return new Proxy(fn.bind(instance), {
    apply: (target, _thisArg, argsList: argsType) => target(...argsList),

    get: (target, prop) => {
      // Delegate to the class instance if the property exists there
      if (prop in instance) {
        return instance[prop as keyof T];
      }
      // Otherwise, look for it on the function
      return target[prop as keyof typeof target];
    }
  });
}

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