reactjs Cannot read property 'keys' of undefined - javascript

I am learning reactjs through a tutorial and ran into this error. That says "Cannot read property 'keys' of undefined" My code is very minimal so I assume that it has to do with the structure of the language. Does anyone know the problem and a possible solution?
<!DOCTYPE html>
<html>
<head>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.0.1/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.0.1/react-dom.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/babel-core/6.1.19/browser.min.js"></script>
<title>ReactJs</title>
</head>
<body>
<div id="app"></div>
<script type="text/babel">
var HelloWorld = ReactDOM.createClass({
render: function() {
return
<div>
<h1>Hello World</h1>
<p>This is some text></p>
</div>
}
});
ReactDOM.render(
<HelloWorld />, document.getElementById('app'));
</script>
</body>
</html>

Edit: oddly, after our comments above, I checked to see if it was indeed the babel core version, I am using this one in my fiddle:
https://cdnjs.cloudflare.com/ajax/libs/babel-core/5.8.24/browser.js
The second I switch to your version above I get this:
Uncaught TypeError: Cannot read property 'keys' of undefined
Use React.createClass not ReactDOM.createClass and wrap multiple lines of html in parenthesis like so:
Working Example: https://jsfiddle.net/69z2wepo/38998/
var Hello = React.createClass({
render: function() {
return (
<div>
<h1>Hello World</h1>
<p>This is some text</p>
</div>
)
}
});
ReactDOM.render(
<Hello name="World" />,
document.getElementById('container')
);

Just to be clear, as the other answers are a bit convoluted. The problem was using "babel-core" instead of "babel-standalone". Just look up for a cdn for babel-standalone instead.
https://cdnjs.cloudflare.com/ajax/libs/babel-standalone/6.26.0/babel.js

Today is my first day with React, and I've faced this issue when I tried to use Babel to transpile the JSX!
The issue is the version you are trying to use, please use this one instead:
<script src="https://cdnjs.cloudflare.com/ajax/libs/babel-standalone/6.25.0/babel.min.js"></script>
Don't forget to write type="text/babel" in the <script> tag which you will write the JSX in to let Babel transpile it for you, if you don't, you will find this error (As I have faced it too! :D):
Uncaught SyntaxError: Unexpected token <

<script src="https://cdnjs.cloudflare.com/ajax/libs/babel-core/5.8.29/browser.js"></script>
This is the version of babel-core which isn't giving me the error as shown below:
If you want to use the latest version, You can use the latest standalone version. (as per 22-Nov-2018)
<script src="https://cdnjs.cloudflare.com/ajax/libs/babel-standalone/6.24.0/babel.js"></script>
But this gives the following warning :
"You are using the in-browser Babel transformer. Be sure to precompile your scripts for production - https://babeljs.io/docs/setup/"

I haven't worked with React before, but there are a few things that I see that may be causing your issues. First, React.createClass instead of ReactDOM.createClass. Second, you need to wrap your html in parentheses:
var HelloWorld = React.createClass({
render: function() {
return (
<div>
<h1>Hello World</h1>
<p>This is some text></p>
</div>
);
}
});
This should get it working

Related

React with Babel without Node

I'm creating a React application without having to use npm or yarn, just want it to work by opening page.html file.
I have this code in both files, cockpit.html:
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<link href="https://raw.githubusercontent.com/cockpit-project/cockpit/master/src/base1/cockpit.css" type="text/plain" rel="stylesheet">
<script src="https://raw.githubusercontent.com/cockpit-project/cockpit/master/src/base1/cockpit.js" type="text/plain"></script>
<script src="https://unpkg.com/react#16/umd/react.development.js" type="text/plain" crossorigin></script>
<script src="https://unpkg.com/react-dom#16/umd/react-dom.development.js" type="text/plain" crossorigin></script>
<script src="https://unpkg.com/babel-standalone#6/babel.min.js" type="text/jsx"></script>
<title>Cockpit Test</title>
</head>
<body>
<div id="root"></div>
<script type="text/babel" src="cockpitTest.jsx"></script>
</body>
</html>
and cockpitTest.jsx:
"use strict";
const rootElement = document.getElementById('root')
class CockpitTest extends React.Component {
componentDidMount() {
console.log("asd")
}
render() {
return (
<div>
<h1>test</h1>
</div>
);
}
}
function App(){
return(
<div>
<CockpitTest name="Test"/>
</div>
)
}
ReactDOM.render(<App />, document.getElementById('rootElement'))
but still I'm getting a blank screen when h1 text is expected. Console doesn't say anything either, it's just blank. Any help would be appreciated!
You have lots of problems
Content-Type
You've set type attributes on all your script and link elements to tell the browser that the CSS and scripts are in formats it doesn't understand. Don't do that.
Only the JSX file itself (in your last <script>) should have a type attribute.
Github is not a hosting service
You are trying to host the cockpit files on raw.github.com. This is not designed to be used as a CDN and returns data with the wrong Content-Type header. Use a real hosting service.
URL
You named the file cockpit.jsx but said src="cockpitTest.jsx"
Missing element
You said document.getElementById('rootElement') but also id="root". These do not match.
You are working without Node.js
The developer tools for React use Node.js to compile it for production-level performance. There's very little reason to not use them all the way through the development process.
First make it a javascript file .js
Then you can either:
Change:
rootElement = document.querySelector('#root'));
AND:
ReactDOM.render(<App />, rootElement)
OR:
ReactDOM.render(<App />, document.querySelector('#root'))
AND:
Delete your constant.
I even got React Router to work, but had problems when it came to separating components out into files for a tidy structure. Couldn't get imports to work inside app.js. Seems like Babel should have helped with imports and exports, but I couldn't get it to work.
Firstly - on your script type your using type "application/babel". This is not a valid media type, you probably want to use "application/javascript". This could be why nothing is displayed.
Secondly - the script you're using is not valid JS, you're using JSX which browsers cannot understand. JSX is what allows us to write html-like tags in JavaScript (the < /> for example). You would either have to write JS instead of JSX, or transpile your JSX using a transpiler such as babel. I would suggest running a compiler such as babel.
Read more about JSX here.

ReactDOM Uncaught SyntaxError: Unexpected token <

I'm sorry to ask such a specific question but I'm working on a simple tutorial which introduces React with the following HTML
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Hello Separate</title>
</script>
</head>
<body>
<h1>Hello Separate</h1>
<div id="app"></div>
</body>
</html>
And a script to create a <p> within the div id ="app" using ReactDOM
ReactDOM.render(
<p>Rendered by React</p>,
document.getElementById("app")
)
I've provided the code in a fiddle here:
I don't understand why I'm getting the error Uncaught SyntaxError: Unexpected token < but think it's coming from the ReactDOM.render function, can anyone provide insight? Thank you!
Two issues with your code,
First
Your scripts are not proper. As per docs, you should add these scripts,
<script src="https://unpkg.com/react#16/umd/react.development.js" crossorigin></script>
<script src="https://unpkg.com/react-dom#16/umd/react-dom.development.js" crossorigin></script>
<script src="https://unpkg.com/babel-standalone#6/babel.min.js"></script>
Second
Might be you are writing your JS code in external JS file.
From the docs,
Now you can use JSX in any <script> tag by adding type="text/babel" attribute to it.
You need to add this script in your HTML file only,
<script type="text/babel">
ReactDOM.render(
<p>Rendered by React</p>,
document.getElementById("app")
)
</script>
Demo
As Emile Bergeron mentioned you're actually writing JSX, so you need 'build'
or transpile the code in regular JavaScript.
However if you're using just JSFiddle, they can transpile the code for you like this.
If you're working locally you can look into create-react-app as they mentioned or babel and webpack to build/bundle your files.
yes you might be right, you will might need to change: <p>Rendered by React</p> to either '<p>Rendered by React</p>' or "<p>Rendered by React</p>"
like this:
ReactDOM.render(
"<p>Rendered by React</p>",
document.getElementById("app")
)
you have to always enclose text or html in ".."

two problems on implementing react without create-react-app?

I am creating a simple react app to practice creating stuffs without dependencies provided by create-react-app (webpack - babel ....)
I am faced with two problems
this is the code:
HTML
<html>
<head><head>
<body>
<div id="App"> </div>
<script type="module" src="script.js" ></script>
<script crossorigin src="https://unpkg.com/react#16/umd/react.production.min.js"></script>
<script crossorigin src="https://unpkg.com/react-dom#16/umd/react-dom.production.min.js"></script>
</body>
</html>
JS
window.onload = () => {
class App extends React.Component {
render() {
return(
<div className="App">
<p>any paragraph</p>
</div>
)
}
}
ReactDom.render(App, document.getElementById('App'))
}
The first problem is:
Nothing is happening when adding the type attribute to the script tag and set its value to "module", nothing works at all, as if js engine could not access the script!!
The second problem:
After removing type="module", it works but with a console error Uncaught SyntaxError: Unexpected token <
So why these two problems happens and how to solve them??
Try loading script.js last. That is, after react-dom is loaded.

ReactJS:cannot display html text on browser

I cannot seem to figure out what I shall do to correct the issue:
I always got no display on the browser, where I expect to see "Hello React".
Here is the HelloWorld code:
ReactDOM.render(Hello, React!,document.getElementById('root'));
You can use following code base to understand basic of React JS (have been used latest version react-15.0.0) -
<!DOCTYPE html>
<html lang="en">
<head>
<title>My First React Example</title>
<!-- use this as script file "fb.me/react-15.0.0.js"
"fb.me/react-dom-15.0.0.js"
cdnjs.cloudflare.com/ajax/libs/babel-core/5.8.34/browser.min.js" -->
</head>
<body>
<div id="greeting-div"></div>
<script type="text/babel">
var Greeting = React.createClass({
render: function() {
return ( <div>{this.props.children} </div>)
}
});
ReactDOM.render(
<div>
<Greeting>hello Aby</Greeting>
<h1>HELLO</h1>
</div>,
document.getElementById('greeting-div') );
</script>
</body>
</html>
check your example here, https://codesandbox.io/s/ElRmqWK5Y
what I will suggest download the react package and run your code there in the beginning, and what I think about your code is you should add react library first than react-dom.
there is a missing < body > in your code , try to add it and tell us if it works
So basically the problem is that you don't transpile your jsx. For your simple example what you can do if you don't want to configure transpiling 'explicitly' with some bundler you can add Babel library and change
<script type="text/jsx">
to
<script type="text/babel">
Let's have a look here, but please remember that jsfiddle uses babel behind (quite sure):
https://jsfiddle.net/69z2wepo/83023/
Also let me paste example from babel docs. Especially take a look for added babel lib + script type.
<div id="output"></div>
<!-- Load Babel -->
<script src="https://unpkg.com/babel-standalone#6/babel.min.js"></script>
<!-- Your custom script here -->
<script type="text/babel">
const getMessage = () => "Hello World";
document.getElementById('output').innerHTML = getMessage();
</script>

React JS Cannot read property 'keys' of undefined

I am beginning to learn React through a tutorial, however I ran into this error when I ran the code that I created.
The error seems to be one that has to do with the framework of the languages. Perhaps with the version of Babel that I imported for the translation.
Does anyone know the actual situation and how to find a soulution.
<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width" />
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.0.1/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.0.1/react-dom.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/babel-core/6.1.19/browser.js"></script>
<title>ReactJs</title>
</head>
<body>
<script type="text/babel">
var HelloWorld = ReactDOM.createClass({
render: function() {
return <div>
<h1>Hello World</h1>
<p>This is some text></p>
</div>
}
});
ReactDOM.render(<HelloWorld/>, document.body);
</script>
</body>
</html>
I'm not sure if you have found the results yet, but I got the same error and found out it's the cdn version mismatch issues.
If you use these cdn's:
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/0.13.3/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/babel-core/5.8.29/browser.js"></script>
and change your
ReactDOM.render(<HelloWorld/>, document.body);
to
React.render(<HelloWorld/>, document.body);
it will work now.
babel-browser is deprecated. use babel-standalone https://github.com/babel/babel-standalone instead:
<script src="https://unpkg.com/babel-standalone#6/babel.min.js"></script>
React.render has been deprecated since React 0.14 (released October 7, 2015):
https://facebook.github.io/react/blog/2015/10/07/react-v0.14.html
I'd strongly recommend the awesome Create React App NPM module from Facebook, which creates React apps with no configuration, but still uses the latest ES6 and Babel features. Also it comes with hot reloading out of the box and has a build option, for creating a minified, bundled .js file ready for production.
https://github.com/facebookincubator/create-react-app

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