What is the correct way to declare a variable with a generic type parameter?

Question

What is the correct way to declare a variable with a generic type parameter?

Exploring the following code snippet that showcases a React component being defined with a type argument named TRow:

function DataTable<TRow> ({ rows: TRow[] }) {
  return (
  )
}

Prior to this implementation, ES6 was utilized and components were created as stateless functions:

const DataTable = ({ rows }) => ( ... )

Is it possible to define a function like this with a generic type argument TRow? Furthermore, does Typescript support this functionality?

generics typescript lambda

Answer 1

Answer №1

Absolutely, it is indeed feasible, however only applicable to Functions and not just any random variable. The key lies in defining generics within the type itself, allowing for the creation of variables that adhere to the generic parameters.

Here are some equivalent examples:

interface Person { age: number }

function Function1<T>({ data }: { data: T[] }): void { return void 0 }
const Function2: <T>({ data }: { data: T[] }) => void = ({data}) => void 0
type  FunctionType = <T>({ data }: { data: T[] }) => void
const Function3: FunctionType = ({data}) => void 0

const b1 = Function1<Person>({data: [{age: 25}]})
const b2 = Function2<Person>({data: [{age: 30}]})
const b3 = Function3<Person>({data: [{age: 35}]})

Answer 2

Absolutely, it is indeed feasible, however only applicable to Functions and not just any random variable. The key lies in defining generics within the type itself, allowing for the creation of variables that adhere to the generic parameters.

Here are some equivalent examples:

interface Person { age: number }

function Function1<T>({ data }: { data: T[] }): void { return void 0 }
const Function2: <T>({ data }: { data: T[] }) => void = ({data}) => void 0
type  FunctionType = <T>({ data }: { data: T[] }) => void
const Function3: FunctionType = ({data}) => void 0

const b1 = Function1<Person>({data: [{age: 25}]})
const b2 = Function2<Person>({data: [{age: 30}]})
const b3 = Function3<Person>({data: [{age: 35}]})

Answer 3

Answer №2

Absolutely, TypeScript allows you to customize your code as desired.

For instance, you can encapsulate your prop types within a generic interface named DataProps with the parameter placeholder Datum (which can represent any type of data).

    interface DataProps<Datum> {
        items: Array<Datum>
    }

Next, if you want to incorporate this property type into a stateless React component class, you can utilize the React.SFC type for referencing such components without states.

    function getDataComponent<Datum>() : React.SFC<DataProps<Datum>>{
        return props => <div>
            <p>{props.items.toString()}</p>
        </div>
    }

This function generates a specific category of stateless React component. To use it,

    const MyStringDataComponent = getDataComponent<string>();

Now, you have a designated data component type, specifically designed for string data. Then, create an instance by

    ReactDOM.render(<MyStringDataComponent items={['a', 'b']} />, document.getElementById('root'))

You should see a,b displayed on your page.

Answer 4

Absolutely, TypeScript allows you to customize your code as desired.

For instance, you can encapsulate your prop types within a generic interface named DataProps with the parameter placeholder Datum (which can represent any type of data).

    interface DataProps<Datum> {
        items: Array<Datum>
    }

Next, if you want to incorporate this property type into a stateless React component class, you can utilize the React.SFC type for referencing such components without states.

    function getDataComponent<Datum>() : React.SFC<DataProps<Datum>>{
        return props => <div>
            <p>{props.items.toString()}</p>
        </div>
    }

This function generates a specific category of stateless React component. To use it,

    const MyStringDataComponent = getDataComponent<string>();

Now, you have a designated data component type, specifically designed for string data. Then, create an instance by

    ReactDOM.render(<MyStringDataComponent items={['a', 'b']} />, document.getElementById('root'))

You should see a,b displayed on your page.

Answer 5

Answer №3

If you want to modify the function definition, you have the option to do so by replacing the function definition with an interface function definition.

For example, consider the following code snippet:

// Instead of this
function DataTable<TRow> ({ rows: TRow[] }) {
    return (
    )
}

// Use this

interface DataTable<TRow> {
    (elements: { rows: TRow[] }): any
}

// Now you can define the function like this:
// (Remember to add <T extends any> to handle .tsx files without syntax errors. For .ts files, <T> is sufficient) 
const myFn: <T>(...args: Parameters<DataTable<T>>) => ReturnType<DataTable<T>> = <T extends any>({ rows: T }) => {
    return 123;
};

// Call the function as follows:

myFn<string>({ rows: ['asd,asd'] });

This response addresses a query related to solving the issue discussed in this thread: Typescript ReturnType of generic function

Answer 6

If you want to modify the function definition, you have the option to do so by replacing the function definition with an interface function definition.

For example, consider the following code snippet:

// Instead of this
function DataTable<TRow> ({ rows: TRow[] }) {
    return (
    )
}

// Use this

interface DataTable<TRow> {
    (elements: { rows: TRow[] }): any
}

// Now you can define the function like this:
// (Remember to add <T extends any> to handle .tsx files without syntax errors. For .ts files, <T> is sufficient) 
const myFn: <T>(...args: Parameters<DataTable<T>>) => ReturnType<DataTable<T>> = <T extends any>({ rows: T }) => {
    return 123;
};

// Call the function as follows:

myFn<string>({ rows: ['asd,asd'] });

This response addresses a query related to solving the issue discussed in this thread: Typescript ReturnType of generic function

What is the correct way to declare a variable with a generic type parameter?

Answer №1

Answer №2

Answer №3

Similar questions

The 'string' Type in Typescript cannot be assigned to the specified type

Unable to modify the Express Request User type, however, I have the ability to incorporate new attributes to Request object

Sending a message through Discord.JS to a designated channel

Adding a timestamp to an array in Angular/Typescript services

How do Angular and NestJS manage to dynamically resolve injection tokens during runtime using the TypeScript type hints provided at compile time?

Ensure that the specified Class type must have a constructor with no arguments

How can I incorporate a feature in my Angular application that allows users to switch between different view types, such as days, using JavaScript

Using Typescript with Protractor for Dropdown Menus

Angular Component Test Results in TypeError Error Failure

What is preventing me from completing this specific task in Kotlin?

What sets a module apart from a script?

Converting an array into an object using Typescript and Angular

Why isn't my Promise fulfilling its purpose?

Testing a React component that uses useParams: A step-by-step guide

Filtering an RXJS BehaviorSubject: A step-by-step guide

Having trouble loading extensive amounts of data into a select element within an Angular application

Bug in auto compilation in Typescript within the Visual Studios 2015

Using custom properties from the Material-UI theme object with custom props in Emotion styled components: a step-by-step guide

Experimenting with PIXI.js and Jest within a React Single Page Application

Is there a way to retrieve the attributes of a generic object using an index in TypeScript?