esm.md

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 to CommonJS.

If your support code is written as ESM, you'll need to use the import configuration option to specify your files, rather than the require option, although we do automatically detect and import any .mjs files found within your features directory.

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:

• Configuration files
• 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.

Transpiling

See Transpiling for how to do just-in-time compilation that outputs ESM.