Automatically replacing/transforming input parameters in cucumber-js

Most implementations of cucumber provide a mechanism for changing literal text in the feature file to values or objects your step definition code can use. This is known as step definition or step argument transforms. Here’s how this works in cucumber-js.

Assume we have this scenario:

Scenario: Test
    When I print 'Welcome {myname}'
    And I print 'Today is {todays_date}'

And we have this step-definition.

defineStep("I print {mystring}", async function (this: OurWorld, x: string) {

Notice the use of {mystring} in the Cucumber expression

We can use defineParameterType() to automatically replace all placeholders.

    regexp: /'([^']*)'/,
    transformer: function (s) {
        return s
            .replace('{todays_date}', new Date().toDateString())
            .replace('{myname}', 'Gerben')
    name: "mystring",
    useForSnippets: false

You can even use this to for objects like so:

    name: 'color',
    regexp: /red|blue|yellow/,
    transformer: s => new Color(s)

defineStep("I fill the canvas with the color {color}", async function (this: OurWorld, x: Color) {
    // x is an object of type Color

When I fill the canvas with the color red