Sung M. Kim

Posted on Nov 26, 2018 • Originally published at slightedgecoder.com on Nov 26, 2018

You don’t always need to import React

#react

r/reactjs has a Weekend Reads, which is a “‘book club’ type thing where we read something every weekend”.

Last week’s topic was JSX In Depth, and I would like to share something that’s been bothering me but learned why.

The question is “why do you import React” when “React” is not used anywhere in your component code?

🎶 Intro

When you start learning react, you might been told to always import React, import React from "React" in your component file.

But that’s not always necessary.

To understand why, let’s see what JSX is.

🤔 JSX?

The subtitle in JSX in Depth describes JSX as

Fundamentally, JSX just provides syntactic sugar for the React.createElement(component, props, ...children) function

You can either use the JSX syntatic sugar 🍬 to create components or use React.createElement directly if you are not transpiling your source code.

🙄 Then shouldn’t you import React everywhere?

No. not unless you use React object for your component.

You can create a “function” component that returns value(s) of a simple JavaScript primitives, such as string or number.

That is the full source for App.js.

In this case, React object is not used anywhere so you can leave out the import statement (but still is a valid component).

📒 Note: If you are creating a class component, you need to import React as it needs to extend React.Component.

And then you can import App.js just like any React component (Line #4).

👋 Parting Words

I hope this has solved for the need to import React for components.

~~99% of the time, you’d use React object in someway to create a component so probably a good idea to import React anyway~~
☝ Forget about this...😅

🏔 Resources

Weekend Reads on r/reactjs – One article per week.
JSX in Depth
See how BabelJS transpiles JSX – Just paste your React code in it.
Demo Sandbox

The post You don’t always need to import React appeared first on Sung's Technical Blog.

Top comments (15)

Alex Young • Dec 1 '18

So here's a question I honestly don't know the answer to: why isn't import React from "react"; inserted at the transpilation step from jsx to js? Why do we need to do this manually? For the case where all you're doing in the file is using jsx tags, the import is confusing and should be unnecessary.

Sung M. Kim • Dec 1 '18 • Edited

Thanks Alex, that's a great question I haven't considered.

Inserting the import statement would require a babel plugin (babel-plugin-react-require or babel-plugin-auto-import, etc), which could relieve us from having to manually insert it where JSX is used.

I honestly didn't know "why" babel doesn't import it automatically so dug around a bit.

It's to prevent import name resolution errors according to following closed issues.

The gist is that, importing react automatically can clash with other imports already declared as "React" or when "React" is declared globally in your application (using "script" tag).

Eugene Karataev • Jun 1 '19

Here's a dirty hack to avoid importing React in every file with JSX. Just add React to window before ReactDOM.render.

import ReactDOM from 'react-dom';
import React from 'react';
import App from './App';

window.React = React;
ReactDOM.render(<App/>, document.querySelector('#mount'));

Now App.js works without throwing a React is not defined error.

// App.js 
export default function() {
  return <div>I am App!</div>
}

This hack is just to illustrate React dependency management. Don't use it in the production code! 😄

Sung M. Kim • Jun 1 '19

Holy mate... Such a convinient hack... You spoiled me 😂

Tried here and worked

Budy • Apr 6 '21

yeep that should do the trick :D, by putting React to the global window object

Amrit Raj • Jan 29 '21

Really Good Explanation.
Just wanted to add that starting from React 17 they have added support for the new JSX-transform. So if you remove the

import React from 'react'

statement for any functional component that returns even jsx (and not simple JS primitives), it will not throw the old

Uncaught ReferenceError: React is not defined

error.
You can read more about it here: reactjs.org/blog/2020/09/22/introd...

Eric Bishard • Nov 27 '18

Short and sweet! Thanks for the good read.

Sung M. Kim • Nov 27 '18

You're welcome & thanks for the feedback.

Learned a lesson from feedbacks what's lacking 😀

Desmond Naranjo • Nov 26 '18

You haven't explained why this would be valuable. There's a lot of stuff I can do that I shouldn't. This seems like one of those stuffs.

Sung M. Kim • Nov 27 '18

You are right Desmond. I wasn't being so clear why it'd be valuable.

My intention was to share what I just learned - the need to import React when it's not used in your code.

So TL;DR should have been "because JSX is transpiled to React.createElement, which requires React to be in scope".

Jenessa White • Oct 24 '19 • Edited

Thanks!
Wondering, if this can help clear up some 'unused variable warnings' even if I am using { useEffect } i don't need to also import react, right?