react-is

What is react-is?

The react-is package is a collection of utilities that allow you to determine the type of a React element. It is useful for type-checking elements and for working with React's different types of components and elements in a more abstract way.

What are react-is's main functionalities?

Type-checking elements

This feature allows you to check if a value is a valid React component type or a React element. It's useful for validating props or for conditional rendering logic.

import { isValidElementType, isElement } from 'react-is';

const MyComponent = () => <div>Hello World</div>;
const myElement = <MyComponent />;

const validType = isValidElementType(MyComponent); // true
const elementCheck = isElement(myElement); // true

Identifying different element types

This feature allows you to identify specific element types like fragments, strict mode wrappers, and portals. This can be useful when writing custom rendering logic or testing components.

import { isFragment, isStrictMode, isPortal } from 'react-is';

const myFragment = <React.Fragment></React.Fragment>;
const myStrictMode = <React.StrictMode></React.StrictMode>;
const myPortal = ReactDOM.createPortal(<div />, document.body);

const fragmentCheck = isFragment(myFragment); // true
const strictModeCheck = isStrictMode(myStrictMode); // true
const portalCheck = isPortal(myPortal); // true

Working with Context

This feature allows you to check if an element is a Context Provider or a Context Consumer. This is particularly useful in higher-order components or in libraries that need to handle context-related elements.

import { isContextConsumer, isContextProvider } from 'react-is';

const MyContext = React.createContext();

const contextProviderCheck = isContextProvider(<MyContext.Provider value={null}></MyContext.Provider>); // true
const contextConsumerCheck = isContextConsumer(<MyContext.Consumer>{() => null}</MyContext.Consumer>); // true

Other packages similar to react-is

prop-types

The prop-types package is used for type-checking props passed to React components. It provides runtime type checking for React props and similar functionality for validating component inputs, but it does not offer the same utilities for identifying React element types as react-is.

enzyme

Enzyme is a testing utility for React that makes it easier to assert, manipulate, and traverse your React Components' output. While it includes methods for type-checking and identifying components, it is more focused on testing utilities rather than providing a comprehensive set of type identifiers like react-is.

README

react-is

This package allows you to test arbitrary values and see if they're a particular React element type.

Installation

# Yarn
yarn add react-is

# NPM
npm install react-is

Usage

Determining if a Component is Valid

import React from "react";
import * as ReactIs from "react-is";

class ClassComponent extends React.Component {
  render() {
    return React.createElement("div");
  }
}

const FunctionComponent = () => React.createElement("div");

const ForwardRefComponent = React.forwardRef((props, ref) =>
  React.createElement(Component, { forwardedRef: ref, ...props })
);

const Context = React.createContext(false);

ReactIs.isValidElementType("div"); // true
ReactIs.isValidElementType(ClassComponent); // true
ReactIs.isValidElementType(FunctionComponent); // true
ReactIs.isValidElementType(ForwardRefComponent); // true
ReactIs.isValidElementType(Context.Provider); // true
ReactIs.isValidElementType(Context.Consumer); // true
ReactIs.isValidElementType(React.createFactory("div")); // true

Determining an Element's Type

Context

import React from "react";
import * as ReactIs from 'react-is';

const ThemeContext = React.createContext("blue");

ReactIs.isContextConsumer(<ThemeContext.Consumer />); // true
ReactIs.isContextProvider(<ThemeContext.Provider />); // true
ReactIs.typeOf(<ThemeContext.Provider />) === ReactIs.ContextProvider; // true
ReactIs.typeOf(<ThemeContext.Consumer />) === ReactIs.ContextConsumer; // true

Element

import React from "react";
import * as ReactIs from 'react-is';

ReactIs.isElement(<div />); // true
ReactIs.typeOf(<div />) === ReactIs.Element; // true

Fragment

import React from "react";
import * as ReactIs from 'react-is';

ReactIs.isFragment(<></>); // true
ReactIs.typeOf(<></>) === ReactIs.Fragment; // true

Portal

import React from "react";
import ReactDOM from "react-dom";
import * as ReactIs from 'react-is';

const div = document.createElement("div");
const portal = ReactDOM.createPortal(<div />, div);

ReactIs.isPortal(portal); // true
ReactIs.typeOf(portal) === ReactIs.Portal; // true

StrictMode

import React from "react";
import * as ReactIs from 'react-is';

ReactIs.isStrictMode(<React.StrictMode />); // true
ReactIs.typeOf(<React.StrictMode />) === ReactIs.StrictMode; // true

Changelog

16.13.1 (March 19, 2020)

React DOM

• Fix bug in legacy mode Suspense where effect clean-up functions are not fired. This only affects users who use Suspense for data fetching in legacy mode, which is not technically supported. (@acdlite in #18238)
• Revert warning for cross-component updates that happen inside class render lifecycles (componentWillReceiveProps, shouldComponentUpdate, and so on). (@gaearon in #18330)