Unable to use Arrow functions inside React component class

Question

I've started a project where I use React JS for the front end an node js in backend. I used webpack for bundling up JS files. I used babel along with other necessary stuff. When I use arrow functions inside a react class, it gives a syntax error, like:

Module build failed: SyntaxError: Unexpected token

But I can use Arrow function in node without any issue.

This is my webpack config file:

import path from 'path';
import webpack from 'webpack';
import 'react-hot-loader/patch';

export default{
  devtool: 'eval',
  entry:[
    'react-hot-loader/patch',
    'webpack-hot-middleware/client?reload=true',
    path.join(__dirname,'client/index.js')],
  output:{
    path:'/',
    publicPath:'/'
  },
  plugins:[
    new webpack.NoErrorsPlugin(),
    new webpack.optimize.OccurenceOrderPlugin(),
    new webpack.HotModuleReplacementPlugin()

  ],
  module:{
    loaders:[
      {
        test:/\.js$/,
        include:path.join(__dirname,'client'),
        loaders: ['react-hot-loader/webpack', 'babel']
      },
      {
        test: /\.jpe?g$|\.gif$|\.svg$|\.png$/i,
        loader: 'file-loader?name=[name].[ext]'
      }
    ]
  },
  resolve:{
    extension:['','.js']
  }
}

My React file:

class mapSidebar extends React.Component{

    constructor(props,context){
       super(props,context);
       this.state = {
         dataSource: []
       };
         this.handleUpdateInput = this.handleUpdateInput.bind (this);
    }

    handleUpdateInput = (value) => {
      this.setState({
        dataSource: [
          value,
          value + value,
          value + value + value,
        ],
      });
    };

    render(){
      return(
        <div>
          <Paper zDepth={2}>
            <div>Hello</div>
            <div>
                <AutoComplete
                  hintText="Type anything"
                  dataSource={this.state.dataSource}
                  onUpdateInput={this.handleUpdateInput}
                />
          </Paper>
        </div>
      );
    }

}

export default mapSidebar;

How to resolve this issue?

Answer 1

It's not the arrow function that's causing a problem here. Class properties are not part of the ES6 specification.

handleUpdateInput = (value) => {
  // ...
};

If you want to be able to transform this code, you'll need to add the class properties babel plugin.

Alternatively, this transform is provided as part of Babel's stage 2 preset.

Using an arrow function with a class property ensures that the method is always invoked with the component as the value for this, meaning that the manual rebinding here is redundant.

this.handleUpdateInput = this.handleUpdateInput.bind (this);