Enum pattern

Use an Enum (or an as const object) when you have a simple list of options that do not carry extra information.

export const SearchMessages = {
	CREATE_INDEX: 'create_index',
	INDEX_READY: 'index_ready',
	SEARCH_INDEX: 'search_index',
	SEARCH_RESULTS: 'search_results',
	SEARCH_RESULTS_EMPTY: 'search_results_empty'
} as const; // <--- The magic bit

// 2. Derive the Type from the object
export type SearchMessagesType = 
    (typeof SearchMessages)[keyof typeof SearchMessages];

Discriminated union

Use a Discriminated Union when each "option" in your list needs to carry different data. This is often called a "Sum Type" or "Tagged Union."

A Discriminated Union requires three things:

1. Types that have a common property (the discriminant).
2. A literal value for that property (e.g., 'success', 'error').
3. A type alias that unions them.

type ApiResponse = 
  | { status: 'loading' } // No extra data
  | { status: 'success', data: string, timestamp: number } // Extra data
  | { status: 'error', message: string, code: number }; // Different extra data

function handleResponse(res: ApiResponse) {
  switch (res.status) {
    case 'loading':
      return 'Spinning...';
    case 'success':
      // TypeScript knows 'data' exists here
      return `Data: ${res.data}`;
    case 'error':
      // TypeScript knows 'message' exists here
      return `Error: ${res.message}`;
  }
}