Trying ES6 style import gives 'Cannot use import statement outside a module'

Question

I am trying to write a javascript test in intellij for which I need to import some dependancies and I want to use ES6 style import statements but getting error

/usr/local/bin/node /workspace/rr-sample/node_modules/mocha/bin/_mocha
--ui bdd --reporter "/Users/me/Library/Application Support/IntelliJIdea2019.1/NodeJS/js/mocha-intellij/lib/mochaIntellijReporter.js"
tests/*.test.js /workspace/rr-sample/tests/App.test.js:3
import chai from 'chai'
^^^^^^

SyntaxError: Cannot use import statement outside a module
    at wrapSafe (internal/modules/cjs/loader.js:1043:16)
    at Module._compile (internal/modules/cjs/loader.js:1091:27)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1160:10)
    at Module.load (internal/modules/cjs/loader.js:976:32)
    at Function.Module._load (internal/modules/cjs/loader.js:884:14)
    at Module.require (internal/modules/cjs/loader.js:1016:19)
    at require (internal/modules/cjs/helpers.js:69:18)
    at /workspace/rr-sample/node_modules/mocha/lib/mocha.js:334:36
    at Array.forEach (<anonymous>)
    at Mocha.loadFiles (/workspace/rr-sample/node_modules/mocha/lib/mocha.js:331:14)
    at Mocha.run (/workspace/rr-sample/node_modules/mocha/lib/mocha.js:809:10)
    at Object.exports.singleRun (/workspace/rr-sample/node_modules/mocha/lib/cli/run-helpers.js:108:16)
    at exports.runMocha (/workspace/rr-sample/node_modules/mocha/lib/cli/run-helpers.js:142:13)
    at Object.exports.handler (/workspace/rr-sample/node_modules/mocha/lib/cli/run.js:292:3)
    at Object.runCommand (/workspace/rr-sample/node_modules/yargs/lib/command.js:242:26)
    at Object.parseArgs [as _parseArgs] (/workspace/rr-sample/node_modules/yargs/yargs.js:1087:28)
    at Object.parse (/workspace/rr-sample/node_modules/yargs/yargs.js:566:25)
    at Object.exports.main (/workspace/rr-sample/node_modules/mocha/lib/cli/cli.js:68:6)
    at Object.<anonymous> (/workspace/rr-sample/node_modules/mocha/bin/_mocha:10:23)
    at Module._compile (internal/modules/cjs/loader.js:1121:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1160:10)
    at Module.load (internal/modules/cjs/loader.js:976:32)
    at Function.Module._load (internal/modules/cjs/loader.js:884:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:67:12)
    at internal/main/run_main_module.js:17:47

What exactly is the issue? I found this link (and others) http://xahlee.info/js/js_import_export.html which tells you how to fix this error but in another context which doesn't help me, and it doesn't explain what the problem is.

In case it is helpful here is the code I am using.

//const chai = require("chai");
import chai from 'chai'

const React = require("react");
const expect = chai.expect;

describe('how it works first-time test', () => {
  it('checks equality', () => {

    const val = false;
    expect(val).to.be.false;
  });

});

Answer 1

The easiest way to run Mocha tests written in ES6 is compiling them on-the-fly using Mocha --require @babel/register option (see https://github.com/mochajs/mocha/wiki/compilers-deprecation#what-should-i-use-instead-then). Of course, you need to make sure to install the corresponding modules and set up the .babelrc accordingly

package.json:

"dependencies": {
  "@babel/cli": "^7.7.4",
  "@babel/core": "^7.7.4",
  "@babel/preset-env": "^7.7.4",
  "@babel/register": "^7.7.4",
...
}

.babelrc:

{
  "presets": [
    [
      "@babel/preset-env"
    ]
  ]
}

See also https://dev.to/bnorbertjs/my-nodejs-setup-mocha--chai-babel7-es6-43ei

Answer 2

I had the same problem when updating one of my ts libraries to es6 modules instead of commonjs. After the change in the tsconfig.json my npm run test produced the mentioned error.

import chai from 'chai'
^^^^^^
SyntaxError: Cannot use import statement outside a module

I solved it without babel by adding an own tsconfig file just for testing.

tsconfig.testing.json

{
  "compilerOptions": {
      "module": "commonjs",
      "target": "es6"
  },
  "include": ["**/*.spec.ts"]
}

To run the tests via script in package.json

"test": "cross-env TS_NODE_PROJECT=\"tsconfig.testing.json\" mocha -r ts-node/register src/**/*.spec.ts",

(cross-env to set the env variable os independent)

Answer 3

I was able to get this working by adding a .mocharc.yaml file at the source of my project with the following:

require: '@babel/register'

source: https://github.com/mochajs/mocha-examples/tree/master/packages/babel

Answer 4

According to the doc:

https://nodejs.org/api/esm.html#esm_code_import_code_statements

So you have to ensure execute the script as an es module.

e.g. Execute the script using babel-node instead of Nodejs to enable the es6 or newer.

Answer 5

For me, I was not able to run it via inline debug option in intellj. So I set extra mocha option and this solved the issue.

--compilers js:babel-core/register

Also, to run via terminal

npx mocha  --compilers js:babel-core/register