all_in_one.ts

export const enum LoadingState {
    INIT = 'INIT',
    LOADING = 'LOADING',
    LOADED = 'LOADED',
}
export interface ErrorState {
    errorMsg: string;
}

export type CallState = LoadingState | ErrorState;

// Helper function to extract error, if there is one.
export function getError(callState: CallState): string | null { 
    if ((callState as ErrorState).errorMsg !== undefined) { 
        return (callState as ErrorState).errorMsg;
    } 
    return null;
}