Typing Object with unknown number of records with consistent type

// dictionary = any number of properties of the same type
interface StringDictionary {
  [key: string]: string;
}

const obj: StringDictionary = {
  key1: "value-1",
  key2: "value-2",
  keyn: "value-n"
};

// record = equivalent to dictionary above
const obj: Record<string, string> = {
  key1: "value-1",
  key2: "value-2",
  keyn: "value-n",
};

Typing object with limited/restricted key definitions

// enums = predefined, but can grow dynamically via the definition
enum KeysEnum {
  FIRST = "firstKey",
  SECOND = "secondKey",
}

type EnumDictionary = Record<KeysEnum, string>;

const obj: EnumDictionary = {
  [KeysEnum.FIRST]: "value1",
  [KeysEnum.SECOND]: "value2",
};

Optional Field

This is to make the variable an optional type.

export interface ISearchResult {  
  title: string;  
  listTitle:string;
  entityName?: string,
  lookupName?:string,
  lookupId?:string  
}

Otherwise, declared variables shows undefined if this variable is not used.

{
  entityName?: string;
}

// equivalent to:
{
  entityName: string | undefined;
}