CODEWITHSUNDEEP
typescript
user991047
user991047

Reputation: 315

typescript understanding the type definitation

I am new to typescript and trying to understand this following code Can someone please help and if there is any good course/book to learn typescript

type ConfigFactoryReturnValue =
  | Record<string, any>
  | Promise<Record<string, any>>;

export type ConfigFactory<
  T extends ConfigFactoryReturnValue = ConfigFactoryReturnValue
> = () => T;

Upvotes: 0

Views: 74

Answers (2)

Amir Saleem
Amir Saleem

Reputation: 3140

Although your question is a bit open-ended and broad still, I'll try to provide some information about the code you've shared.

// The type keyword is used to define a type, for example
type MyCustomType = string;

// Record<K, T> is a Utility type for handling objects.
// Record defines the type of key:value pair.

// This means that MyRecord is an object whose keys are string and can have any value
type MyRecord = Record<string, any>;

// Promise is used to determine a Promise type, which means a method which returns a Promise
// Promise<T> is the syntax in which T determines the type of returned value when promise is resolved

// ConfigFactoryReturnValue is a Type which can be an object of type string:any or promise<Object<string, any>>
type ConfigFactoryReturnValue = Record<string, any> | Promise<Record<string, any>>;

// The Type T extends ConfigFactoryReturnValue signifies that Generic type T must satisfy the type
// ConfigFactoryReturnValue i.e. along with other keys it should have keys defined in ConfigFactoryReturnValue
export type ConfigFactory<T extends ConfigFactoryReturnValue> = () => T;

as far as the Typescript course/book is concerned, there are plenty of courses available online on platforms like Udemy, Coursera, etc.

Upvotes: 2

mtdot
mtdot

Reputation: 312

The first block combined between type alias and union type, that means you defined your own data type name ConfigFactoryReturnValue and that data type can be Record<string, any> or Promise<Record<string, any>>

type ConfigFactoryReturnValue =
  | Record<string, any>
  | Promise<Record<string, any>>;

The second block combining type alias with generics feature of typescript. That means exporting alias type of a generic type.

<T extends ConfigFactoryReturnValue = ConfigFactoryReturnValue> define that the type T should extend from ConfigFactoryReturnValue or is instance of ConfigFactoryReturnValue as default.

export type ConfigFactory<
  T extends ConfigFactoryReturnValue = ConfigFactoryReturnValue
> = () => T;

Upvotes: 1

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