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ES Modules (experimental)

You can optionally write your support code (steps, hooks, etc) with native ES modules syntax - i.e. using import and export statements without transpiling. This is enabled without any additional configuration, and you can use either of the .js or .mjs file extensions.

Example (adapted from our original example):

// features/support/steps.mjs
import { Given, When, Then } from '@cucumber/cucumber'
import { strict as assert } from 'assert'

Given('a variable set to {int}', function (number) {
  this.setTo(number)
})

When('I increment the variable by {int}', function (number) {
  this.incrementBy(number)
})

Then('the variable should contain {int}', function (number) {
  assert.equal(this.variable, number)
})

As well as support code, these things can also be in ES modules syntax:

  • Custom formatters
  • Custom snippets

You can use ES modules selectively/incrementally - so you can have a mixture of CommonJS and ESM in the same project.

When using a transpiler for e.g. TypeScript, ESM isn't supported - you'll need to configure your transpiler to output modules in CommonJS syntax (for now).

The config file referenced for Profiles can only be in CommonJS syntax. In a project with type=module, you can name the file cucumber.cjs, since Node expects .js files to be in ESM syntax in such projects.