TypeScript
TypeScript Utility Types Explained
Partial, Required, Readonly, Pick, Omit, Record, NonNullable, Extract, Exclude Types
In TypeScript, there are multiple built-in utility (default) types. It would be a good thing to know they exist because they are handy in some situations. Some are easier to understand than others. I am going to explain them in a short and simple way, so everyone can understand them.
1 — Partial
The first one is Partial, this can make all properties optional in a type where properties originally should be required.
type Worker = {
name: string;
profession: string;
}// Not defining 'profession' is allowed
const worker: Partial<Worker> = {
name: 'Jeroen'
}
2 — Required
The opposite one of Partial is Required, instead of making properties optional, it makes them required.
type Worker = {
name?: string;
profession?: string;
}// You should defining 'name' and 'profession'
const worker: Required<Worker> = {
name: 'Jeroen',
profession: 'Developer',
}
3 — Readonly
With Readonly, you prevent that properties are going to be re-assigned.
type Worker = {
name: string;
profession: string;
}const worker: Readonly<Worker> = {
name: 'Jeroen',
profession: 'Developer',
}worker.name = 'Bob'; // Not allowed
4 — Pick
A more advanced utility type is Pick, which can be used to include only a few properties.
type Worker = {
name: string;
profession: string;
isWorking: boolean;
}// Only 'name' and 'isWorking' are included
const worker: Pick<Worker, 'name' | 'isWorking'> = {
name: 'Jeroen',
isWorking: true,
}
5 — Omit
The opposite way of the Pick type is called Omit, you exclude the properties you don’t want to use.
type Worker = {
name: string;
profession: string;
isWorking: boolean;
}
