[TypeScript] Create Explicit and Readable Type Declarations with TypeScript mapped Type Modifiers

Using the optional “+” sign together with mapped type modifiers, we can create more explicit and readable type declarations. We can also use the “-” (minus) sign to remove optional declarations from properties.

For example, we have an interface:

interface IPet {

    name: string;

    age: number;

    favoritePark?: string

}

There is two required props and one favoriatePark as optional prop.

From TypeScirpt 2.8, we are able to gereate a new interface based on existing one, and add or remove props:

For example we want to remove all the optional props, we can use '-':

interface IPetRequired {

  [K in keyof IPET]-?: IPet[K]

}

'-': remove

'?': optional

'-?': remove optional

We can also use '+' to indicate what we have added:

type ReadonlyPet = {

    +readonly [K in keyof IPet]?: IPet[K]

}

Here we added readonly type.

巴特西

[TypeScript] Create Explicit and Readable Type Declarations with TypeScript mapped Type Modifiers

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