Functional Cucumber.js

functional-cucumber-steps.js

const { defineStep } = require('cucumber');
const arity = require('util-arity');

/**
 * Wrap a step function so it is passed the `world` scope as the first argument.
 * Allows writing step definitions in a "purer" more functional style without
 * worry about what `this` is, which is especially annoying when calling functions
 * from other functions.
 *
 * Internal helpers expect world as the first argument, which is fine when they're
 * calling each other, this is just to wrap the initial step definition function.
 *
 * Internally you can also choose to just pass bits of the world, for example driver
 * helpers can just be passed the driver.
 *
 * Need to return a function with corrected arity as cucumber checks
 * the arity matches it's expectations. The arity is shortened by one to
 * ignore the first argument i.e. the reference to `this`.
 * @see https://github.com/cucumber/cucumber-js/issues/514
 *
 * @param {Function} fn - the function to wrap
 * @return {Function}
 */
function withWorld (fn) {
  return arity(fn.length - 1, function () { return fn(this, ...arguments); });
}

/**
 * Helper to go to URL.
 *
 * @param {IWebDriver} driver
 * @param {String} url
 * @return {Promise}
 */
function gotoUrl (driver, url) {
  return driver.get(url);
}

/**
 * Helper to go to Google home page.
 *
 * @param {Object} world
 * @return {Promise}
 */
function gotoGoogle (world) {
  return gotoUrl(world.driver, 'https://google.com');
}

// Define cucumber step - `withWorld` is only used on the initial method, internally it is passed.
defineStep('I visit Google', withWorld(gotoGoogle));