Author: John Au-Yeung

Sometimes, we want to add type aliases with TypeScript.

In this article, we’ll look at how to add type aliases with TypeScript.

How to add type aliases with TypeScript?

To add type aliases with TypeScript, we can use the type keyword.

For instance, we write

type PrimitiveArray = Array<string | number | boolean>;

to create the PrimitiveArray type with the type keyword which is an array with string, number, or boolean entries.

Conclusion

To add type aliases with TypeScript, we can use the type keyword.

Sometimes, we want to make a single property optional in TypeScript.

In this article, we’ll look at how to make a single property optional in TypeScript.

How to make a single property optional in TypeScript?

To make a single property optional in TypeScript, we can use the Optional type.

For instance, we write

type MakePersonInput = Optional<Person, "nickname">;

to create the MakePersonInput type that makes the nickname property in the Person interface optional.

Conclusion

To make a single property optional in TypeScript, we can use the Optional type.

Sometimes, we want to create a strongly typed array of arrays in TypeScript.

In this article, we’ll look at how to create a strongly typed array of arrays in TypeScript.

How to create a strongly typed array of arrays in TypeScript?

To create a strongly typed array of arrays in TypeScript, we can nest the Array type.

For instance, we write

const x: Array<Array<Foo>> = [];

to declare variable x with the nested array entries having the Foo type with Array<Array<Foo>>.

Conclusion

To create a strongly typed array of arrays in TypeScript, we can nest the Array type.

Sometimes, we want to add types to class constructor in TypeScript.

In this article, we’ll look at how to add types to class constructor in TypeScript.

How to add types to class constructor in TypeScript?

To add types to class constructor in TypeScript, we can use the typeof operator to get the type from the class.

For instance, we write

class Zoo {
  constructor(public AnimalClass: typeof Animal) {
    const a = new AnimalClass();
  }
}

to use typeof Animal to return the type for the Animal class automatically.

Then we can assume that AnimalClass is the Animal class and instantiate it in the constructor.

Conclusion

To add types to class constructor in TypeScript, we can use the typeof operator to get the type from the class.

Sometimes, we want to add functions to an enum with TypeScript.

In this article, we’ll look at how to add functions to an enum with TypeScript.

How to add functions to an enum with TypeScript?

To add functions to an enum with TypeScript, we can create a class that has an enum has its instance variable.

For instance, we write

enum Mode {
  landscape,
  portrait,
}

class Device {
  constructor(public mode: Mode) {
    console.log(Mode[this.mode]);
  }
}

to add the Device class that takes a Mode variable as the argument of its constructor.

Then we can use Mode[this.mode] to get a value dynamically from the Mode enum.

Conclusion

To add functions to an enum with TypeScript, we can create a class that has an enum has its instance variable.