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I am following the official reactjs instructions to create a sample app. My node version is 6.9.0.
I created sample react app which is supposed to display a empty tic tac toe table according to the official website using following instructions:
npm install -g create-react-app
create-react-app my-app
cd my-app
changed to my-app directory
removed the default files inside the source directory as directed. Now my index.js looks like this
import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
Then I ran yarn start
But all I see is blank screen no tic tac toe table. And couple warnings in the console saying
Compiled with warnings.
./src/index.js
Line 1: 'React' is defined but never used no-unused-vars
Line 2: 'ReactDOM' is defined but never used no-unused-vars
Search for the keywords to learn more about each warning.
To ignore, add // eslint-disable-next-line to the line before.
596
After Babel transformed your code which is written with JSX elements, into the React. createElement calls, you can see where React is used. If you forget to import React, it will be undefined and the createElement call will fail. So make sure to always import React in your functional components too!
JSX is not a requirement for using React. Using React without JSX is especially convenient when you don't want to set up compilation in your build environment. Each JSX element is just syntactic sugar for calling React.
The React. js error "X is not defined react/jsx-no-undef" occurs when we forget to import a function, class or a variable in our code before using it. To solve the error, make sure to import the value before using it in your code, e.g. import {myFunc} from 'my-package' . Copied!
You should create some component/element/, maybe style it, then call ReactDOM to render your component to the underlying html and then you will have it.
React is used to handle JSX and creation of React componentReactDOM in your simple case will be used to render created element to dom.See here : https://reactjs.org/blog/2015/10/01/react-render-and-top-level-api.html
So ading something like
ReactDOM.render(
<h1>Hello, world!</h1>,
document.getElementById('root')
);
to your code, you will get something if in your index.html there is element with id="root" inside <body> tag
124
You missed last parts in steps 4 & 5:
- Add a file named index.css in the src/ folder with this CSS code.
- Add a file named index.js in the src/ folder with this JS code.
index.css
body {
font: 14px "Century Gothic", Futura, sans-serif;
margin: 20px;
}
ol, ul {
padding-left: 30px;
}
.board-row:after {
clear: both;
content: "";
display: table;
}
.status {
margin-bottom: 10px;
}
.square {
background: #fff;
border: 1px solid #999;
float: left;
font-size: 24px;
font-weight: bold;
line-height: 34px;
height: 34px;
margin-right: -1px;
margin-top: -1px;
padding: 0;
text-align: center;
width: 34px;
}
.square:focus {
outline: none;
}
.kbd-navigation .square:focus {
background: #ddd;
}
.game {
display: flex;
flex-direction: row;
}
.game-info {
margin-left: 20px;
}
index.js
class Square extends React.Component {
render() {
return (
<button className="square">
{/* TODO */}
</button>
);
}
}
class Board extends React.Component {
renderSquare(i) {
return <Square />;
}
render() {
const status = 'Next player: X';
return (
<div>
<div className="status">{status}</div>
<div className="board-row">
{this.renderSquare(0)}
{this.renderSquare(1)}
{this.renderSquare(2)}
</div>
<div className="board-row">
{this.renderSquare(3)}
{this.renderSquare(4)}
{this.renderSquare(5)}
</div>
<div className="board-row">
{this.renderSquare(6)}
{this.renderSquare(7)}
{this.renderSquare(8)}
</div>
</div>
);
}
}
class Game extends React.Component {
render() {
return (
<div className="game">
<div className="game-board">
<Board />
</div>
<div className="game-info">
<div>{/* status */}</div>
<ol>{/* TODO */}</ol>
</div>
</div>
);
}
}
// ========================================
ReactDOM.render(
<Game />,
document.getElementById('root')
);
This simply means your project has eslint configured to catch unused variables.
If you use JSX or anything React within that file the warning will go away just like suggested by zmii in his answer.
But i am writing this answer because someone showed me their code and they were facing the same problem.
Their code :
import React from 'react';
const person = () => {
return "<h2>I am a person!</h2>"
};
export default person;
The problem in the above code was that while returning, he used double quotes. So instead of JSX, it was returning string and therefore they were getting error that React was never not used.
Conclusion: Syntax are important so keep in mind, specially if you are starting out.
Hope this helps someone.
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