webpack: import + module.exports in the same module caused error

I'm developing a website with webpack. When I have a code like this:

import $ from 'jquery';
function foo() {};
module.exports = foo;

I got the error Uncaught TypeError: Cannot assign to read only property 'exports' of object '#<Object>'.

Turns out that changing import $ from 'jquery' to var $ = require('jquery') don't cause any errors.

Why import with module.exports causes this error? Is anything wrong in using require instead?

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最佳答案

You can't mix import and module.exports. In the import world, you need to export things.

// Change this
module.exports = foo;


// To this
export default foo;
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This happens if other modules down stream have an unexpected require tree. Babel changes require to import where it isn't supposed to which causes the aforementioned issue @Matthew Herbst. To solve this add "sourceType": "unambiguous" to your babelrc file or babel.config.js so that @babel/plugin-transform-runtime won't do this change of require expression to import in your commonjs files. eg:

module.exports = {
presets: [
'@quasar/babel-preset-app'
],


"sourceType": "unambiguous"
}
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You can use require with export. But not import and module.exports.

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In my react-native-web case, just use an additional webpack rule, then the TypeError: Cannot assign to read only property 'exports' of object is fixed. Maybe you can ref to it.

npm install --save-dev react-app-rewired

Create a config-overrides.js in your project root

// used by react-app-rewired


const webpack = require('webpack');
const path = require('path');


module.exports = {
webpack: function (config, env) {
config.module.rules[1].use[0].options.baseConfig.extends = [
path.resolve('.eslintrc.js'),
];


// To let alias like 'react-native/Libraries/Components/StaticRenderer'
// take effect, must set it before alias 'react-native'
delete config.resolve.alias['react-native'];
config.resolve.alias['react-native/Libraries/Components/StaticRenderer'] =
'react-native-web/dist/vendor/react-native/StaticRenderer';
config.resolve.alias['react-native'] = path.resolve(
'web/aliases/react-native',
);


// Let's force our code to bundle using the same bundler react native does.
config.plugins.push(
new webpack.DefinePlugin({
__DEV__: env === 'development',
}),
);


// Need this rule to prevent `Attempted import error: 'SOME' is not exported from` when `react-app-rewired build`
// Need this rule to prevent `TypeError: Cannot assign to read only property 'exports' of object` when `react-app-rewired start`
config.module.rules.push({
test: /\.(js|tsx?)$/,
// You can exclude the exclude property if you don't want to keep adding individual node_modules
// just keep an eye on how it effects your build times, for this example it's negligible
// exclude: /node_modules[/\\](?!@react-navigation|react-native-gesture-handler|react-native-screens)/,
use: {
loader: 'babel-loader',
},
});


return config;
},
paths: function (paths, env) {
paths.appIndexJs = path.resolve('index.web.js');
paths.appSrc = path.resolve('.');
paths.moduleFileExtensions.push('ios.js');
return paths;
},
};

Also create a web/aliases/react-native/index.js

// ref to https://levelup.gitconnected.com/react-native-typescript-and-react-native-web-an-arduous-but-rewarding-journey-8f46090ca56b


import {Text as RNText, Image as RNImage} from 'react-native-web';
// Let's export everything from react-native-web
export * from 'react-native-web';


// And let's stub out everything that's missing!
export const ViewPropTypes = {
style: () => {},
};
RNText.propTypes = {
style: () => {},
};
RNImage.propTypes = {
style: () => {},
source: () => {},
};


export const Text = RNText;
export const Image = RNImage;
// export const ToolbarAndroid = {};
export const requireNativeComponent = () => {};

Now you can just run react-app-rewired start instead of react-scripts start


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