Mapped Types in Typescript

This post will explore Mapped Types, another advanced feature of the Typescript type system. It is part of the Introduction to Advanced Types in TypeScript series.

A useful mental model to have when approaching some of the advanced type system features of Typescript is to view them as a mechanism for constructing other types from existing types. This view is spot on when it comes to mapped types as they are a mechanism that Typescript provides by constructing new types by mapping existing types into new ones.

This post would show how this looks like. It would be as beginner-friendly as possible, but having some knowledge of Generics, Union Types and Literal types in Typescript would be a plus.

To kickstart we take a quick again, at the keyof Operator, as it is essential to the workings of Mapped Types.

Conditional Types in Typescript

This post is about conditional types in typescript, which happens to be an interesting and powerful feature of the typescript's type system. It is part of the Introduction to Advance Types in TypeScript series.

Conditional types can be seen as a mechanism that allows us to perform ternary operations on types. 

Normally, ternary operations work with values, for example:

resulting value == true ? value A : value B
let value = 10
const isEven = value % 2 == 0 ? true : false

Conditional types gives us the ability to perform similar operation on types. Where we get a type out of two possibility, depending on the outcome of a check. 

any, unknown and never types in Typescript

This post will be a quick overview of three interesting types in Typescript: any, unknown, and never with the aim of quickly explaining what they are, and when to use them. It is part of the Introduction to Advance Types in TypeScript series.  

To start with, it is a good mental model to view Types from the perspective of set theory. This idea is fully explored in Union and Intersection Types in TypeScript, but for a quick summary, the idea is simple. When types are created, see it as similar to defining a Set. And what do sets contain? they contain objects. The next thing is to see values as objects that belongs to a set. A value defined to be part of a set, would not be allowed in a different set which it does not belong in or overlap with. 

Tuple Types in TypeScript

In this post, we would be looking at tuple types in TypeScript. It will also touch on generic rest parameters and variadic tuple types which are two of the advanced parts of tuple types.