Declare a functional component as "pure" - reactjs

Question

How to signal to React that a functional component is "pure", as an equivalent of React.PureComponent for component classes?
function C(props) {
return <var>{props.n}</var>
}
without making it a class
class C extends React.PureComponent {
render() {
return <var>{this.props.n}</var>
}
}

Answer 1

As of React 16.6.0, memo has been added, so the answer is now:
const C = React.memo(props => {
return <var>{props.n}</var>
})

Answer 2

Based on the concept of purity in functional programming paradigms, a function is pure if:
Its return value is only determined by its input values
Its return value is always the same for the same input values
There seem two ways to do it for React functional components:
Using memo from react:
import React, { memo } from 'react';
const Component = (props) {
return (
// Component code
)
}
// Wrap component using "memo" HOC
export default memo(Component);
Using pure from recompose:
import React from 'react';
import { pure } from 'recompose';
const Component = (props) {
return (
// Component code
)
}
// Wrap component using "pure" HOC
export default pure(Component);

Answer 3

To #Shubham and #Andrew:
No, functional components are not PureComponents. Functional components will always get re-render if the parent component re-renders. A PureComponent contains a default shouldComponentUpdate() and I think that's what OP wants.
You can use pure provided by recompose to wrap and optimize your functional components:
import pure from 'recompose/pure'
const YourFunctionalComponent = (props) => {
...
}
export default pure(YourFunctionalComponent)

Answer 4

In addition to CodinCat answer.
The author of the library, recomponse, wrote a note on 25th Oct of 2018, where he stated, that what he tried to solve by the library was solved by the React Team through introducing hooks. Not only that, React team added optimization feature like React.memo(), which was named as React.pure() earlier. So, it's time to use React.memo(). Read Official Docs about it