Cypress ParseError: 'import' 和 'export' 可能只出现在 'sourceType: module'

Question

I updated Cypress from 3.0.3 to 3.1.3 . Im using ES6 import/export modules which must be working related to docs. But Im getting a line with undefined in terminal and following error in the GUI:

<root_dir>/node_modules/@babel/runtime/helpers/esm/defineProperty.js:1
export default function _defineProperty(obj, key, value) {
^
ParseError: 'import' and 'export' may appear only with 'sourceType: module'

My tests are in vanilla JS, no TS os CoffeeScript. Im stuck, in 3.0.3 it worked fine.

Answer 1

This error is caused by the presence of modern keywords like "import" and "export" when Cypress runs in the browser. Unlike Selenium or Protractor -- it actually runs inside the browser. Since browsers don't support modern JS yet, you'll need to use webpack or browserify to transpile your code.

https://docs.cypress.io/api/plugins/preprocessors-api.html#Examples

Here is a fantastic blog post on how to get Cypress to work with modern JS and Typescript using webpack: https://glebbahmutov.com/blog/use-typescript-with-cypress/

^^ The post is focused on TypeScript, but the configuration options for Javascript will be similar.

The following npm packages must be installed and in your package.json:

"@cypress/webpack-preprocessor": "^4.1.0",
"cypress": "^3.3.1",
"ts-loader": "^6.0.3",
"typescript": "^3.5.2",
"webpack": "^4.34.0"

Webpack should be installed using:

npm install --save-dev webpack typescript ts-loader
npm install --save-dev @cypress/webpack-preprocessor

The following should be present under the "compilerOptions" section of a file called tsconfig.json in your root directory, with "allowJs" set to true for non-typescript users:

"module": "es6",
"target": "es6",
"types": ["cypress"],
"allowJs": true

A file called "webpack.config.js" should be present in your root directory with the following:

const path = require('path')

module.exports = {
  entry: './src/index.ts',
  module: {
    rules: [
      {
        test: /\.tsx?$/,
        use: 'ts-loader',
        exclude: /node_modules/
      }
    ]
  },
  resolve: {
    extensions: ['.tsx', '.ts', '.js']
  },
  output: {
    filename: 'bundle.js',
    path: path.resolve(__dirname, 'dist')
  }
}

And these exports should be present under cypress/plugins/index.js:

const webpack = require('@cypress/webpack-preprocessor')
module.exports = on => {
  const options = {
    // send in the options from your webpack.config.js, so it works the same
    // as your app's code
    webpackOptions: require('../../webpack.config'),
    watchOptions: {}
  }

  on('file:preprocessor', webpack(options))
}

Note this final bit at the end of the Cypress plugins file,

on('file:preprocessor', webpack(options))

That is where Cypress is told to process your modern JS code in such a way as to make it Cypress-runnable.

Answer 2

I solved it, in my root folder was a babel.config.js file which possibly overrode Cypress configs. After I deleted it, everything is working. ¯\_(ツ)_/¯

Update: Maybe the magic was readd the babel.config.js with this content based on this issue: https://github.com/cypress-io/cypress/issues/2945

module.exports = process.env.CYPRESS_ENV
  ? {}
  : { presets: ['@vue/babel-preset-app'] }

Answer 3

In case people are coming here for the message...

ParseError: 'import' and 'export' may appear only with 'sourceType: module'

... in a Cypress TypeScript project. Here is the answer:

Cypress does support TypeScript out of the box, as long as you have a tsconfig.json file. However, imports don't work unless you preprocess your TypeScript files.

Here are the steps:

1. Install webpack: yarn add -D webpack
2. Install ts-loader: yarn add -D ts-loader
3. Install @cypress/webpack-preprocessor: yarn add -D @cypress/webpack-preprocessor

Now, make sure you have these 3 files, tsconfig.json , webpack.config.js and plugins/index.js on your Cypress folder.

plugins/index.js :

const wp = require("@cypress/webpack-preprocessor");

module.exports = on => {
    const options = {
        webpackOptions: require("../webpack.config.js")
    };
    on("file:preprocessor", wp(options));
};

tsconfig.json :

{
  "compilerOptions": {
    "strict": true,
    "target": "es5",
    "lib": ["es5", "dom"],
    "types": ["cypress"]
  },
  "include": [
    "**/*.ts"
  ]
}

webpack.config.js :

module.exports = {
    mode: 'development',
    resolve: {
        extensions: ['.ts', '.js']
    },
    module: {
        rules: [
            {
                test: /\.ts$/,
                exclude: [/node_modules/],
                use: [
                    {
                        loader: 'ts-loader',
                        options: {
                            // skip typechecking for speed
                            transpileOnly: true
                        }
                    }
                ]
            }
        ]
    }
}

It should just work now.

Answer 4

When using @vue/cli you can simply do (which is commented in Cypress /plugins/index.js ):

const webpack = require('@cypress/webpack-preprocessor');

module.exports = (on, config) => {
    on('file:preprocessor', webpack({
        webpackOptions: require('@vue/cli-service/webpack.config'),
        watchOptions: {},
    }));
};

Answer 5

There is an official sample on github available at this address https://github.com/cypress-io/cypress-example-recipes/tree/master/examples/preprocessors__typescript-webpack

Note: if you are on windows and want to run localy the project , first update the path in the package.json.

// D:\path\cypress-example-recipes\examples\preprocessors__typescript-webpack\package.json

{
  "name": "cypress-example-typescript-webpack",
  "version": "1.0.0",
  "description": "Example showing TypeScript tests with Cypress",
  "scripts": {
    // ...
    "cypress:open": "..\\..\\node_modules\\.bin\\cypress open"
  }
}