Is it possible to test ES6 Modules with Jest without esm or babel? Since node v13 supports es6 natively have tried:
//package.json { … "type": "module" … } //__tests__/a.js import Foo from '../src/Foo.js'; $ npx jest Jest encountered an unexpected token … Details: /home/node/xxx/__tests__/a.js:1 import Foo from '../src/Foo.js'; ^^^^^^ SyntaxError: Cannot use import statement outside a module When babel is added a transpiler, it works, but can es6 modules be used natively as well?
Yes, it is possible from [email protected]. From this version, there is a native support of esm, so you will not have to transpile your code with babel anymore.
It is not documented yet, but according to this issue you have to do 3 easy steps to achieve that (At the time of writing this answer):
import statements by setting transform: {} in your jest config filenode@^12.16.0 || >=13.2.0 with --experimental-vm-modules flagjest-environment-node or jest-environment-jsdom-sixteen.So your jest config file should contain at least this:
export default { testEnvironment: 'jest-environment-node', transform: {} ... }; And to set --experimental-vm-modules flag, you will have to run Jest from package.json as follows (I hope this will change in the future):
"scripts": { "test": "node --experimental-vm-modules node_modules/jest/bin/jest.js" } I hope, this answer was helpful to you.
jest name isn't available within the test module. I'm sure there are other problems too as per the linked issue. Sadly it looks like Babel is the way to go for now.
transform I get the following error SyntaxError: Cannot use import statement outside a module
jest object "can also be imported explicitly via import {jest} from '@jest/globals'" jestjs.io/docs/en/jest-object
"type": "module" in the package.json and running node with --experimental-vm-modules was enough (Jest 26.6.3 and node v14.15.4). Also a little cleaner way to specify the test command: "test": "NODE_OPTIONS=--experimental-vm-modules jest"Note that this is is still experimental, but we have documented how to test this, so there's hopefully less confusion.
https://jestjs.io/docs/en/ecmascript-modules
The steps in https://stackoverflow.com/a/61653104/1850276 are correct
I followed the tips provided in the accepted answer, but I added the property "type": "module" in my package.json in order to jest works properly. This is what I done:
In package.json:
"devDependencies": { "jest": "^26.1.0", "jest-environment-jsdom-sixteen": "^1.0.3", "jest-environment-node": "^26.1.0" }, "scripts": { "test": "node --experimental-vm-modules node_modules/jest/bin/jest.js" }, "type": "module", "jest": { "transform": {}, "testEnvironment": "jest-environment-jsdom-sixteen" } To run jest from "jest" extension in VSCode with "--experimental-vm-modules" flags, put this config in your global or workspaces settings.json:
"jest.nodeEnv": { "NODE_OPTIONS": "--experimental-vm-modules" } In addition to @Radovan Kuka's answer, here's how to run Jest with ES modules, using npx:
"test:monitoring": "npx --node-arg=--experimental-vm-modules jest -f monitoring.test.js --detectOpenHandles", The benefit is that one doesn't need to provide the absolute node_modules path.
npx out of the commands and everything's working fine.
Without Babel, here's a complete, minimal example that works on recent Jest versions. Run with npm test.
$ tree -I node_modules . ├── package.json ├── src │ └── foo.js └── __tests__ └── foo.spec.js package.json:
{ "type": "module", "scripts": { "test": "NODE_OPTIONS=--experimental-vm-modules jest" }, "devDependencies": { "jest": "^29.3.1" } } src/foo.js:
export const bar = () => 42; __tests__/foo.spec.js:
import {bar} from "../src/foo"; describe("foo.bar()", () => { it("should return 42", () => { expect(bar()).toBe(42); }); }); The secret sauce is in the package.json: "type": "module" and NODE_OPTIONS=--experimental-vm-modules jest.
If you want to add a mock, it's a bit complicated. See this answer.
