We can't compare them exactly. There are differences in use case.

(2018 update)

ReactJS

React has as its main focus Web Development.

React’s virtual DOM is faster than the conventional full refresh model, since the virtual DOM refreshes only parts of the page. You can reuse code components in React, saving you a lot of time. (You can in React Native too.) As a business: The rendering of your pages completely, from the server to the browser will improve the SEO of your web app. It improves the debugging speed making your developer’s life easier. You can use hybrid mobile app development, like Cordova or Ionic, to build mobile apps with React, but is more efficiently building mobile apps with React Native from many points.

React Native

An extension of React, niched on Mobile Development.

Its main focus is all about Mobile User Interfaces. iOS & Android are covered. Reusable React Native UI components & modules allow hybrid apps to render natively. No need to overhaul your old app. All you have to do is add React Native UI components into your existing app’s code, without having to rewrite. Doesn't use HTML to render the app. Provides alternative components that work in a similar way, so it wouldn't be hard to understand them. Because your code doesn’t get rendered in an HTML page, this also means you won’t be able to reuse any libraries you previously used with React that renders any kind of HTML, SVG or Canvas. React Native is not made from web elements and can’t be styled in the same way. Goodbye CSS Animations!

Hopefully I helped you :)

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I know there are already many answers to it but after reading all these I felt no one explains what is the architectural difference between these two and how these two works so I believe there is still room for explanation.

React

React = Vanilla JS + ES6 + HTML + CSS = JSX = Web Apps(Front end)

So let's talk about React first because React-Native is also based on react and the same concept of JS is been used there.

React is a JS library which is used to make beautiful, flexible, performant single page web applications, So now a question will appear in your mind what is single page web app.

Single-Page Application

A single-page application is an app that works inside a browser and does not require page reloading during use. You are using these types of applications every day. These are, for instance: Gmail, Google Maps, Facebook, or GitHub. SPAs are all about serving an outstanding UX by trying to imitate a “natural” environment in the browser — no page reloads, no extra wait time. It is just one web page that you visit which then loads all other content using JavaScript — which they heavily depend on. SPA requests the markup and data independently and renders pages straight in the browser. We can do this thanks to advanced JavaScript frameworks like AngularJS, Ember.js, Meteor.js, Knockout.js, React.js, Vue.js. Single-page sites help keep the user in one, comfortable web space where content is presented to the user in a simple, easy, and workable fashion.

How it works

Now you know what is SPA, So as you know it's a web app so it will use HTML elements for running into the browser and also used JS for handling all the functionality related to these elements. It used Virtual DOM to render new changes in the components.

React-Native

Now you have a bit of an idea about react so let's talk about react-native

React-Native = React (Vanilla JS + ES6 + Bridge between JS and Native code) + Native(iOS, Android) = Mobile Apps(Android, iOS, also supported web but have some limitations)

React-Native is used to make beautiful cross-platform mobile apps(Android, iOS) using React.

How it works

In React-Native there are two threads.

JS Thread Native Thread

All of the React code is executed inside JS thread and the final value passes to the native thread which draws a layout on the screen with the final value.

JS thread performs all of the calculations and passes data to native, How?

React uses an Async Bridge to pass data to Native thread in JSON format is called React-Native

So we use Native components for making a presentational view in react-native and use that bridge to communicate between these two different worlds.

JS thread is fast enough to execute JavaScript and the native thread is also fast enough to execute native code but as React used the async bridge to communicate between these two worlds, overloading this bridge causes performance issues.

Update: React-Native is now going through re-architecuter phase and facebook team is trying to remove async bridge to communicate between JS and native synchronously the major part of this re-architecuter is JSI(Javascript interface) and fabirc.

JSI: JSI removes the need for a bridge between Native(Java/ObjC) and Javascript code. It also removes the requirement to serialize/deserialize all the information as JSON for communication between the two worlds. JSI is opening doors to new possibilities by bringing closes the javascript and the native worlds.

Below are the main things which JSI is offers.

Javascript Interface which allows us to register methods with the Javascript runtime. These methods are available via the global object in the Javascript world. The methods can be entirely written in C++ or they can be a way to communicate with Objective C code on iOS and Java code in Android. Any native module that is currently using the traditional bridge for communication between Javascript and the native worlds can be converted to a JSI module by writing a simple layer in C++ On iOS writing this layer is simple because C++ can run directly in Objective C hence all the iOS frameworks and code is available to use directly. On android however we have to go an extra mile to do this through JNI. These methods can be fully synchronous which means using async/await is not mandatory.

Fabric: Fabirc is a new UI layer which allows us to communicate with the native UI components synchronous, According to the docs.

Fabric is React Native's new rendering system, a conceptual evolution of the legacy render system. The core principles are to unify more render logic in C++, improve interoperability with host platforms, and to unlock new capabilities for React Native. Development began in 2018 and in 2021, React Native in the Facebook app is backed by the new renderer.

Let's talk about the common and differences between these two frameworks.

Feature React React-Native Platform Web Android, IOS, Web Open Source Yes Yes User Interface HTML + CSS Native Components(iOS, Android, Web) Architecture Virtual DOM Virtual DOM + Bridge + Native implementation Animations CSS Animations Native Animations Styling CSS JS Stylesheets Developed By Facebook Facebook

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In a simple sense, React and React native follows the same design principles except in the case of designing user interface.

React native has a separate set of tags for defining user interface for mobile, but both use JSX for defining components. Both systems main intention is to develop re-usable UI-components and reduce development effort by its compositions. If you plan & structure code properly you can use the same business logic for mobile and web

Anyway, it's an excellent library to build user interface for mobile and web.

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React is a declarative, efficient, and flexible JavaScript library for building user interfaces.Your components tell React what you want to render – then React will efficiently update and render just the right components when your data changes. Here, ShoppingList is a React component class, or React component type.

A React Native app is a real mobile app. With React Native, you don't build a “mobile web app”, an “HTML5 app”, or a “hybrid app”. You build a real mobile app that's indistinguishable from an app built using Objective-C or Java. React Native uses the same fundamental UI building blocks as regular iOS and Android apps.

More info

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ReactJS is a core framework, meant to build component isolated based on reactive pattern, you can think of it as the V from MVC, although I would like to state that react does brings a different feel, specially if you are less familiar with reactive concept.

ReactNative is another layer that is meant to have a set component for Android and iOS platform that are common. So the code looks basically the same as ReactJS because is ReactJS, but it load natively in mobile platforms. You can also bridge more complex and platform relative API with Java/Objective-C/Swift depending on the OS and use it within React.

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React Native is primarily developed in JavaScript, which means that most of the code you need to get started can be shared across platforms. React Native will render using native components. React Native apps are developed in the language required by the platform it targets, Objective-C or Swift for iOS, Java for Android, etc. The code written is not shared across platforms and their behavior varies. They have direct access to all features offered by the platform without any restriction.

React is an open-source JavaScript library developed by Facebook for building user interfaces. It's used for handling view layer for web and mobile apps. ReactJS used to create reusable UI components.It is currently one of the most popular JavaScript libraries in the it field and it has strong foundation and large community behind it.If you learn ReactJS, you need to have knowledge of JavaScript, HTML5 and CSS.

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React is the base abstraction of React Native and React DOM, so if your going to work with React Native you will also need React... same with the web but instead of React Native you will need React DOM.

Since React is the base abstraction the general syntax and workflow is the same but the components that you would use are very different thus you will need to learn those differences this is inline with React so called moto which is "Learn once write anywhere" because if you know React(base abstraction) you could simply learn the differences between platform without learning another programming language, syntax and workflow.

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React-Native is a framework, where ReactJS is a javascript library you can use for your website.

React-native provides default core components (images, text), where React provides a bunch of components and make them work together.

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React Native is for mobile applications while React is for websites(front-end). Both are frameworks invented by Facebook. React Native is a cross platform developing framework meaning one could write almost the same code for both IOS and Android and it would work. I personally know much more about React Native so I will leave it at this.

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React Js is a Javascript Library where you can develop and run faster web applications using React .

React Native lets you build mobile apps using only JavaScript,it is used for Mobile application development . more info here https://facebook.github.io/react-native/docs/getting-started.html

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In regards to component lifecycle and all the other bells and whistles it is mostly the same.

The difference mostly is the JSX markup used. React uses one that resembles html. The other is markup that is used by react-native to display the view.

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React Js is manipulating with HTML Dom. But React native is manipulating with mobile(iOS/android) native ui component.

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ReactJS is a javascript library which is used to build web interfaces. You would need a bundler like webpack and try to install modules you would need to build your website.

React Native is a javascript framework and it comes with everything you need to write multi-platform apps (like iOS or Android). You would need xcode and android studio installed to build and deploy your app.

Unlike ReactJS, React-Native doesn't use HTML but similar components that you can use accross ios and android to build your app. These components use real native components to build the ios and android apps. Due to this React-Native apps feel real unlike other Hybrid development platforms. Components also increases reusability of your code as you don't need to create same user interface again on ios and android.

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In simple terms ReactJS is parent library which returns something to render as per the host-environment(browser, mobile, server, desktop..etc). Apart from rendering it also provides other methods like lifecycle hooks.. etc.

In the browser, it uses another library react-dom to render DOM elements. In mobile, it uses React-Native components to render platform specific(Both IOS and Android) native UI components. SO,

react + react-dom = web developement

react + react-native = mobile developement

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A little late to the party, but here's a more comprehensive answer with examples:

React

React is a component based UI library that uses a "shadow DOM" to efficiently update the DOM with what has changed instead of rebuilding the entire DOM tree for every change. It was initially built for web apps, but now can be used for mobile & 3D/vr as well.

Components between React and React Native cannot be interchanged because React Native maps to native mobile UI elements but business logic and non-render related code can be re-used.

ReactDOM

Was initially included with the React library but was split out once React was being used for other platforms than just web. It serves as the entry point to the DOM and is used in union with React.

Example:

import React from 'react';
import ReactDOM from 'react-dom';

class App extends Component {
    state = {
        data: [],
    }

    componentDidMount() {
        const data = API.getData(); // fetch some data
        this.setState({ data })
    }

    clearData = () => {
        this.setState({
            data: [],
        });
    }

    render() {
        return (
            <div>
                {this.state.data.map((data) => (
                    <p key={data.id}>{data.label}</p>
                ))}
                <button onClick={this.clearData}>
                    Clear list
                </button>
            </div>
        );
    }

}

ReactDOM.render(App, document.getElementById('app'));

React Native

React Native is a cross-platform mobile framework that uses React and communicates between Javascript and it's native counterpart via a "bridge". Due to this, a lot of UI structuring has to be different when using React Native. For example: when building a list, you will run into major performance issues if you try to use map to build out the list instead of React Native's FlatList. React Native can be used to build out IOS/Android mobile apps, as well as for smart watches and TV's.

Expo

Expo is the go-to when starting a new React Native app.

Expo is a framework and a platform for universal React applications. It is a set of tools and services built around React Native and native platforms that help you develop, build, deploy, and quickly iterate on iOS, Android, and web apps

Note: When using Expo, you can only use the Native Api's they provide. All additional libraries you include will need to be pure javascript or you will need to eject expo.

Same example using React Native:

import React, { Component } from 'react';
import { Flatlist, View, Text, StyleSheet } from 'react-native';

export default class App extends Component {
    state = {
        data: [],
    }

    componentDidMount() {
        const data = API.getData(); // fetch some data
        this.setState({ data })
    }

    clearData = () => {
        this.setState({
            data: [],
        });
    }

    render() {
        return (
            <View style={styles.container}>
                <FlatList
                    data={this.state.data}
                    renderItem={({ item }) => <Text key={item.id}>{item.label}</Text>}
                />
                <Button title="Clear list" onPress={this.clearData}></Button>
            </View>
        );
    }

}

const styles = StyleSheet.create({
    container: {
        flex: 1,
    },
});

Differences:

Notice that everything outside of render can remain the same, this is why business logic/lifecycle logic code can be re-used across React and React Native

In React Native all components need to be imported from react-native or another UI library

Using certain API's that map to native components are usually going to be more performant than trying to handle everything on the javascript side. ex. mapping components to build a list vs using flatlist

Subtle differences: things like onClick turn into onPress, React Native uses stylesheets to define styles in a more performant way, and React Native uses flexbox as the default layout structure to keep things responsive.

Since there is no traditional "DOM" in React Native, only pure javascript libraries can be used across both React and React Native

React360

It's also worth mentioning that React can also be used to develop 3D/VR applications. The component structure is very similar to React Native. https://facebook.github.io/react-360/

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https://i.stack.imgur.com/j3TPA.png

ReactJS

React is used for creating websites, web apps, SPAs etc.

React is a Javascript library used for creating UI hierarchy.

It is responsible for rendering of UI components, It is considered as V part Of MVC framework.

React’s virtual DOM is faster than the conventional full refresh model, since the virtual DOM refreshes only parts of the page, Thus decreasing the page refresh time.

React uses components as basic unit of UI which can be reused this saves coding time. Simple and easy to learn. React Native

React Native is a framework that is used to create cross-platform Native apps. It means you can create native apps and the same app will run on Android and ios.

React native have all the benefits of ReactJS

React native allows developers to create native apps in web-style approach.

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REACT is Javascript library to build large/small interface web application like Facebook.

REACT NATIVE is Javascript framework to develop native mobile application on Android, IOS, and Windows Phone.

Both are open sourced by Facebook.

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Here is a very nice explanation:

Reactjs is a JavaScript library that supports both front-end and server. Furthermore, it can be used to create user interfaces for mobile apps and websites.

React Native is a cross-platform mobile framework that uses Reactjs for building apps and websites. React Native compiles to native app components enables the programmer to build mobile applications that can run on different platforms such as Windows, Android, iOS in JavaScript.

Reactjs can be described as a base derivative of React DOM, for the web platform while React Native is a base derivative in itself, which means that the syntax and workflow remain the same, but components alter.

Reactjs, eventually, is a JavaScript library, which enables the programmer to create an engaging and high performing UI Layer while React Native is an entire framework for building cross-platform apps, be it web, iOS or Android.

In Reactjs, virtual DOM is used to render browser code in Reactjs while in React Native, native APIs are used to render components in mobile.

The apps developed with Reactjs renders HTML in UI while React Native uses JSX for rendering UI, which is nothing but javascript.

CSS is used for creating styling in Reactjs while a stylesheet is used for styling in React Native.

In Reactjs, the animation is possible, using CSS, just like web development while in React Native, an animated API is used for inducing animation across different components of the React Native application.

If the need is to build a high performing, dynamic, and responsive UI for web interfaces, then Reactjs is the best option while if the need is to give mobile apps a truly native feeling, then React Native is the best option.

More here: https://www.simform.com/reactjs-vs-reactnative/

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Here are the differences that I know about:

They have different html tags: React Native is using for handling text and instead of in React. React Native is using Touchable components instead of a regular button element. React Native has ScrollView and FlatList components for rendering lists. React Native is using AsyncStorage while React is using local storage. In React Native routers function as a stack, while in React, we use Route components for mapping navigation.

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In summary: React.js for Web Development while React-Native for Mobile App Development

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React Js - React JS is front-end javascript library it's large library not a framework

It follows the component based approach which helps in building reusable UI components It is used for developing complex and interactive web and mobile UI Even though it was open-sourced only in 2015, it has one of the largest communities supporting it.

It is used for developing complex and interactive web and mobile UI

Even though it was open-sourced only in 2015, it has one of the largest communities supporting it.

ReactNative - React Native is an open-source mobile application framework.

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Some differences are as follows: 1- React-Native is a framework which used to create Mobile Apps, where ReactJS is a javascript library you can use for your website. 2- React-Native doesn’t use HTML to render the app while React uses. 3- React-Native used for developing only Mobile App while React use for website and Mobile.

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A simple comparison should be

ReactJs

return(
    <div>
      <p>Hello World</p>
    </div>
)

React Native

return(
    <View>
      <Text>Hello World</Text>
    </View>
)

React Native don't have Html Elements like div, p, h1, etc, instead it have components that make sense for mobile.
More details at https://reactnative.dev/docs/components-and-apis

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React Native is a JavaScript framework and it comes with everything you need to write multi-platform apps (like iOS or Android).

ReactJS is a JavaScript library which is used to build web interfaces and build your website.

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