CODEWITHSUNDEEP
javascriptreactjs
ankur
ankur

Reputation: 4733

Uncaught error in bundle.js for reactjs

I am getting started with react js, Build my first component i am stuck on this error 

"Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined."

The editor i am using is visual studio 2017 for this.

code for webpack.config.js is 

module.exports = {
  context: __dirname,
  entry: "./app.js",
  output: {
    path: __dirname + "/dist",
    filename: "bundle.js"
  },
  watch: true,
  module: {
    rules: [{
      test: /\.js$/,
      exclude: /node_modules/,
      use:
        {
          loader: 'babel-loader',
          options: {
            presets: ['babel-preset-env', 'babel-preset-react', ]
          }
        }
    }
    ]
  }
}

app.js 

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

ReactDOM.render(
    <Button />,
    document.getElementById('root')
);

class Button extends React.Component {
    render() {
        return (<button>42</button>);
    }
}

the page that i am rendering is index.cshtml

@{
    ViewBag.Title = "Index";
    Layout = "~/Views/Shared/_Layout.cshtml";
}

<h2>Index test</h2>

<div id="root"></div>

@section scripts{

    <script src="~/Scripts/React/dist/bundle.js"></script>
}

After i make a change in app.js,next step is to got to cmd prompt and do npm run webpack.

Thanks for the help

Upvotes: 0

Views: 2349

Answers (1)

supra28
supra28

Reputation: 1636

You are using the component before declaring it. This doesn't work because the javascript classes don't get hoisted. This should work

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

class Button extends React.Component {
    render() {
        return (<button>42</button>);
    }
}

ReactDOM.render(
    <Button />,
    document.getElementById('root')
);

Upvotes: 2

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