Typing Object

Source

// 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",
};

// enums
enum KeysEnum {
  FIRST = "firstKey",
  SECOND = "secondKey",
}

type EnumDictionary = Record<KeysEnum, string>;

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

Typing Index Key

Without explicit declaration of key as index, the key passed to an object via object[key] will result in type error

const allTypes = {
  "thisthing": "",
  "anotherthing": "",
  "something": "find this",
};

const lookUpKey = "something";

const valueToLookFor = allTypes[lookUpKey as keyof typeof allTypes]

Combining Static and Dynamic Keys

interface MixedDictionary {
  // static
  staticKey: string;
  // dynamic = dictionary
  [key: string]: string | number;
}

const obj: MixedDictionary = {
  staticKey: "staticValue",
  dynamicKey1: "value-1",
  dynamicKey2: "value-2",
  dynamicKeyn: "value-n",
};