how to solve this error You may need an appropriate loader to handle this file type

问题

I got this error with this library https://github.com/react-native-web-community/react-native-web-linear-gradient/

the error link https://github.com/react-native-web-community/react-native-web-linear-gradient/issues/1 details of error: Module parse failed: Unexpected token (5:22) You may need an appropriate loader to handle this file type.

my webpack:

'use strict';

const autoprefixer = require('autoprefixer');
const path = require('path');
const webpack = require('webpack');
const HtmlWebpackPlugin = require('html-webpack-plugin');
const CaseSensitivePathsPlugin = require('case-sensitive-paths-webpack-plugin');
const InterpolateHtmlPlugin = require('react-dev-utils/InterpolateHtmlPlugin');
const WatchMissingNodeModulesPlugin = require('react-dev-utils/WatchMissingNodeModulesPlugin');
const eslintFormatter = require('react-dev-utils/eslintFormatter');
const ModuleScopePlugin = require('react-dev-utils/ModuleScopePlugin');
const getClientEnvironment = require('./env');
const paths = require('./paths');

const publicPath = '/';
const publicUrl = '';
const env = getClientEnvironment(publicUrl);

module.exports = {
  devtool: 'cheap-module-source-map',
  entry: [
    require.resolve('./polyfills'),
    require.resolve('react-dev-utils/webpackHotDevClient'),
    paths.appIndexJs,
  ],
  output: {
    pathinfo: true,
    filename: 'static/js/bundle.js',
    chunkFilename: 'static/js/[name].chunk.js',
    publicPath: publicPath,
    devtoolModuleFilenameTemplate: info =>
      path.resolve(info.absoluteResourcePath).replace(/\\/g, '/'),
  },
  resolve: {
    modules: ['node_modules', paths.appNodeModules].concat(
      process.env.NODE_PATH.split(path.delimiter).filter(Boolean)
    ),
    extensions: ['.web.js', '.mjs', '.js', '.json', '.web.jsx', '.jsx'],
    alias: {
      'babel-runtime': path.dirname(
        require.resolve('babel-runtime/package.json')
      ),
      'react-native': 'react-native-web',
      'react-native-linear-gradient': 'react-native-web-linear-gradient'
    },
    plugins: [
      new ModuleScopePlugin(paths.appSrc, [paths.appPackageJson]),
    ],
  },
  module: {
    strictExportPresence: true,
    rules: [
      {
        test: /\.(js|jsx|mjs)$/,
        enforce: 'pre',
        use: [
          {
            options: {
              formatter: eslintFormatter,
              eslintPath: require.resolve('eslint'),
              baseConfig: {
                extends: [require.resolve('eslint-config-react-app')],
              },
              ignore: false,
              useEslintrc: false,
            },
            loader: require.resolve('eslint-loader'),
          },
        ],
        include: paths.appSrc,
      },
      {
        oneOf: [
          {
            test: [/\.bmp$/, /\.gif$/, /\.jpe?g$/, /\.png$/],
            loader: require.resolve('url-loader'),
            options: {
              limit: 10000,
              name: 'static/media/[name].[hash:8].[ext]',
            },
          },
          {
            test: /\.(js|jsx|mjs)$/,
            include: paths.appSrc,
            loader: require.resolve('babel-loader'),
            options: {
              babelrc: false,
              presets: [require.resolve('babel-preset-react-app')],
              cacheDirectory: true,
            },
          },
          {
            test: /\.css$/,
            use: [
              require.resolve('style-loader'),
              {
                loader: require.resolve('css-loader'),
                options: {
                  importLoaders: 1,
                },
              },
              {
                loader: require.resolve('postcss-loader'),
                options: {
                  ident: 'postcss',
                  plugins: () => [
                    require('postcss-flexbugs-fixes'),
                    autoprefixer({
                      browsers: [
                        '>1%',
                        'last 4 versions',
                        'Firefox ESR',
                        'not ie < 9', // React doesn't support IE8 anyway
                      ],
                      flexbox: 'no-2009',
                    }),
                  ],
                },
              },
            ],
          },
          {
            exclude: [/\.js$/, /\.html$/, /\.json$/],
            loader: require.resolve('file-loader'),
            options: {
              name: 'static/media/[name].[hash:8].[ext]',
            },
          },
        ],
      },
    ],
  },
  plugins: [
    new InterpolateHtmlPlugin(env.raw),
    new HtmlWebpackPlugin({
      inject: true,
      template: paths.appHtml,
    }),
    new webpack.NamedModulesPlugin(),
    new webpack.DefinePlugin(env.stringified),
    new webpack.HotModuleReplacementPlugin(),
    new CaseSensitivePathsPlugin(),
    new WatchMissingNodeModulesPlugin(paths.appNodeModules),
    new webpack.IgnorePlugin(/^\.\/locale$/, /moment$/),
  ],
  node: {
    dgram: 'empty',
    fs: 'empty',
    net: 'empty',
    tls: 'empty',
    child_process: 'empty',
  },
  performance: {
    hints: false,
  },
};

the class who make the problem:

import React, { PureComponent } from 'react';
import { View } from 'react-native';

export default class LinearGradient extends PureComponent {
  static defaultProps = {
    start: {
      x: 0.5,
      y: 0,
    },
    end: {
      x: 0.5,
      y: 1,
    },
    locations: [],
    colors: [],
  };

  state = {
    width: 1,
    height: 1,
  };

  measure = ({ nativeEvent }) =>
    this.setState({
      width: nativeEvent.layout.width,
      height: nativeEvent.layout.height,
    });

  getAngle = () => {
    // Math.atan2 handles Infinity
    const angle =
      Math.atan2(
        this.state.width * (this.props.end.y - this.props.start.y),
        this.state.height * (this.props.end.x - this.props.start.x)
      ) +
      Math.PI / 2;
    return angle + 'rad';
  };

  getColors = () =>
    this.props.colors
      .map((color, index) => {
        const location = this.props.locations[index];
        let locationStyle = '';
        if (location) {
          locationStyle = ' ' + location * 100 + '%';
        }
        return color + locationStyle;
      })
      .join(',');

  render() {
    return (
      <View
        style={[
          this.props.style,
          { backgroundImage: `linear-gradient(${this.getAngle()},${this.getColors()})` },
        ]}
        onLayout={this.measure}
      >
        {this.props.children}
      </View>
    );
  }
}

static defaultProps and ()=> make the bug so what could be wrong?

回答1:

Partial fix >>

Steps:

1-npm install babel babel-cli --save-dev on the library

2-I add "transpile": "babel src/index.js --out-file src/index-transpiled.js" in package.json scripts

3-yarn transpile

4-I moved the ES5 file to my code and it worked

Update - Full Fix

I included my src folder and the libraries to babel too

// Process JS with Babel.
          {
            test: /\.(js|jsx|mjs)$/,
            include: [
              /src\/*/,
              /node_modules\/react-native-/,
            ],
            loader: require.resolve('babel-loader'),
            options: {
              babelrc: false,
              presets: [require.resolve('babel-preset-react-native')],
              cacheDirectory: true
            }
          },

回答2:

I think this is because of ES7 feature. Do you have stage-0 installed & added to your .babelrc or webpack.config.js file?

Here how you can do it:

npm i --save-dev babel-preset-stage-0 And then you should include it into webpack.config.js file like below:

loader: "babel-loader", // or just "babel"
query: {
  presets: [ <other presets>, 'stage-0']
}

Or add it to .babelrc file:

{
  "presets": ["stage-0"]
}

UPDATE

As I said earlier the issue belongs to ES7 feature. Seems like webpack can not resolve static keyword within react-native-web-linear-gradient module. So what I did to fix this issue:

I copied the source code from react-native-web-linear-gradient into my own component called LinearGradient. I didn't change anything within it.
I installed stage-0 and added it to .babelrc as i described above.
Later instead of using react-native-web-linear-gradient i use my LinearGradient component.

As a result i got gradient on my page. git project link.

Hope it will help!

回答3:

This is how webpack can be configured to load assets, such as images (pngs, svgs, jpgs and so on):

npm install --save-dev file-loader
Add this in the webpack.config.js, under the module.exports.rules:

{
  test: /\.(png|svg|jpg|gif)$/,
  use: ["file-loader"]
}

Now, when you import MyImage from './my-image.png', that image will be processed and added to your output directory and the MyImage variable will contain the final url of that image after processing.

来源：https://stackoverflow.com/questions/48034538/how-to-solve-this-error-you-may-need-an-appropriate-loader-to-handle-this-file-t

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react-native

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babel

react-native-web