The ts-essentials from dozoisch

ts-essentials

All essential TypeScript types in one place 🤙

Install

npm add --save-dev ts-essentials

yarn add --dev ts-essentials

What's inside?

Basic
- Primitive
Dictionaries
- Dictionary
- DictionaryValues
Deep Partial & DeepRequired & Deep Readonly
Writable & DeepWritable
Omit
OmitProperties
NonNever
Merge
MarkRequired
UnionToIntersection
Opaque types
Tuple constraint
Literal types
Exhaustive switch cases
ValueOf
AsyncOrSync

Basic:

Primitive type matching all primitive values.

Dictionaries

const stringDict: Dictionary<string> = {
  a: "A",
  b: "B",
};

// Specify second type argument to change dictionary keys type
const dictOfNumbers: Dictionary<string, number> = {
  420: "four twenty",
  1337: "HAX",
};

// You may specify union types as key to cover all possible cases. It acts the same as Record from TS's standard library
export type DummyOptions = "open" | "closed" | "unknown";
const dictFromUnionType: Dictionary<number, DummyOptions> = {
  closed: 1,
  open: 2,
  unknown: 3,
};

// and get dictionary values
type stringDictValues = DictionaryValues<typeof stringDict>;
// Result: string

Deep Partial & Deep Required & Deep Readonly

type ComplexObject = {
  simple: number;
  nested: {
    a: string;
    array: [{ bar: number }];
  };
};

type ComplexObjectPartial = DeepPartial<ComplexObject>;
const samplePartial: ComplexObjectPartial = {
  nested: {
    array: [{}],
  },
};

type ComplexObjectAgain = DeepRequired<ComplexObjectPartial>;
const sampleRequired: ComplexObjectAgain = {
  simple: 5,
  nested: {
    a: "test",
    array: [],
  },
};

type ComplexObjectReadonly = DeepReadonly<ComplexObject>;

Writable

Make all attributes of object writable.

type Foo = {
  readonly a: number;
  readonly b: string;
};

const foo: Foo = ({ a: 1, b: "b" }(foo as Writable<typeof foo>).a = 42);

type Foo = {
  readonly foo: string;
  bar: {
    readonly x: number;
  };
}[];

const test: DeepWritable<Foo> = [
  {
    foo: "a",
    bar: {
      x: 5,
    },
  },
];

// we can freely write to this object
test[0].foo = "b";
test[0].bar.x = 2;

Omit

type ComplexObject = {
  simple: number;
  nested: {
    a: string;
    array: [{ bar: number }];
  };
};

type SimplifiedComplexObject = Omit<ComplexObject, "nested">;

// Result:
// {
//  simple: number
// }

// if you want to Omit multiple properties just use union type:
type SimplifiedComplexObject = Omit<ComplexObject, "nested" | "simple">;

// Result:
// { } (empty type)

OmitProperties

Removes all properties extending type P in type T.

interface Example {
  log(): void;
  version: string;
}

type ExampleWithoutMethods = OmitProperties<Example, Function>;

// Result:
// {
//   version: string;
// }

// if you want to Omit multiple properties just use union type like

type ExampleWithoutMethods = OmitProperties<Example, Function | string>;
// Result:
// { } (empty type)

NonNever

Useful for purifying object types. It improves intellisense but also allows for extracting keys satisfying a conditional type.

type GetDefined<TypesMap extends { [key: string]: any }> = keyof NonNever<
  { [T in keyof TypesMap]: TypesMap[T] extends undefined ? never : TypesMap[T] }
>;

Merge

type Foo = {
  a: number;
  b: string;
};

type Bar = {
  b: number;
};

const xyz: Merge<Foo, Bar> = { a: 4, b: 2 };
// Result:
// {
//   a: number,
//   b: number,
// }

MarkRequired

Useful when you're sure some optional properties will be set. A real life example: when selecting an object with its related entities from an ORM.

class User {
  id: number;
  posts?: Post[];
  photos?: Photo[];
}
type UserWithPosts = MarkRequired<User, 'posts'>;

// example usage with a TypeORM repository -- `posts` are now required, `photos` are still optional
async function getUserWithPosts(id: number): Promise<UserWithPosts> {
  return userRepo.findOneOrFail({ id }, { relations: ['posts'] }) as Promise<UserWithPosts>;
}

UnionToIntersection

Useful for converting mapped types with function values to intersection type (so in this case - overloaded function).

type Foo = {
  bar: string;
  xyz: number;
};

type Fn = UnionToIntersection<{ [K in keyof Foo]: (type: K, arg: Foo[K]) => any }[keyof Foo]>;

Opaque types

type PositiveNumber = Opaque<number, "positive-number">;

function makePositiveNumber(n: number): PositiveNumber {
  if (n <= 0) {
    throw new Error("Value not positive !!!");
  }
  return (n as any) as PositiveNumber; // this ugly cast is required but only when "producing" opaque types
}

Tuple constraint

function foo<T extends Tuple>(tuple: T): T {
  return tuple;
}

const ret = foo(["s", 1]);
// return type of [string, number]

You can also parametrize Tuple type with a type argument to constraint it to certain types, i.e. Tuple<string | number>.

Literal types

For TypeScript >= 3.4: TypeScript 3.4 shipped const assertions which are very similar to our literal helper but also make type readonly, you should prefer as const construct.

For TypeScript < 3.4: this is served as a backport of the const assertions added since TypeScript 3.4.

// prevent type widening https://blog.mariusschulz.com/2017/02/04/typescript-2-1-literal-type-widening
const t = {
  letter: literal("a"), // type stays "a" not string
  digit: literal(5), // type stays 5 not number
};

Exhaustive switch cases

function actOnDummyOptions(options: DummyOptions): string {
  switch (options) {
    case "open":
      return "it's open!";
    case "closed":
      return "it's closed";
    case "unknown":
      return "i have no idea";
    default:
      // if you would add another option to DummyOptions, you'll get error here!
      throw new UnreachableCaseError(options);
  }
}

ValueOf type

const obj = {
  id: "123e4567-e89b-12d3-a456-426655440000",
  name: "Test object",
  timestamp: 1548768231486,
};

type objKeys = ValueOf<typeof obj>;
// Result: string | number

AsyncOrSync type

Useful as a return type in interfaces or abstract classes with missing implementation

interface CiProvider {
  getSHA(): AsyncOrSync<string>;
  // same as
  getSHA(): Promise<string> | string;
}

class Circle implements CiProvider {
  // implementation can use sync version
  getSHA() {
    return "abc";
  }
}

class Travis implements CiProvider {
  // implementation can use async version when needed
  async getSHA() {
    // do async call
    return "def";
  }
}

Contributors

Thanks goes to these wonderful people (emoji key):

_{Chris Kaczor} 💻 💼 💡 📖	_{Xiao Liang} 💻 🤔 📖	_{Mateusz Burzyński} 💻 🤔 📖	_{Maciej Bembenista} 💻 🤔 📖	_{Michael Tontchev} 💻 🤔 📖	_{Thomas den Hollander} 💻 🤔 📖	_{Esa-Matti Suuronen} 💻 🤔 📖
_{Ilya Semenov} 💻 🤔 📖	_{Code Checks} 👀	_{Patricio Palladino} 🤔	_{Artur Kozak} 💻 🤔