Transpiling

Step definitions and support files can be written in syntax/language that compiles to JavaScript, and just-in-time compiled when you run Cucumber.

For example, you might want to use Babel:

This would mean any support code loaded with the require option would be transpiled first.

TypeScript

Your tsconfig.json should have these compilerOptions on:

"allowSyntheticDefaultImports": true,
"resolveJsonModule": true,

Other than that, a pretty standard TypeScript setup should work as expected.

You'll also need to specify where your support code is, since .ts files won't be picked up by default.

If you are using ts-node:

In a configuration file { requireModule: ['ts-node/register'], require: ['step-definitions/**/*.ts'] }
On the CLI $ cucumber-js --require-module ts-node/register --require 'step-definitions/**/*.ts'

For ESM projects, you can use ts-node's ESM loader and then import your TypeScript files:

$ NODE_OPTIONS"--loader ts-node/esm" cucumber-js --import 'step-definitions/**/*.ts'

Don't forget to set your tsconfig.json to emit JavaScript with import and export statements:

{
  "compilerOptions": {
    "module": "esnext"
  }
}

If you are using babel with @babel/preset-typescript:

In a configuration file { requireModule: ['@babel/register'], require: ['step-definitions/**/*.ts'] }
On the CLI $ cucumber-js --require-module @babel/register --require 'step-definitions/**/*.ts'

See ESM for general advice on using loaders for transpilation in ESM projects.