How Googles text adventure commands work

Recently I rediscovered my love for text-based and point-and-click adventures from days gone. Digging around what I wanted to play next, I came across an easter egg Google put in place in 2018: A text adventure!

All I needed to do was to visit google.com, entering the search term “text adventure” and then… well, nothing.

This text adventures happens within the developer tools, so a quick press of Command+Option+J (or Ctrl+Shift+J for Windows and Linux) and I was greeted with this message:

> Would you like to play a game? (yes/no)

How exciting!!!

Just typing yes would get the game started.

> Type single word commands, no need to describe the subject.
> For example, "grab banana peel" should just be "grab" or "use banana peel" should just be "use"

Hold on a second! I can invoke functionality just by writing keywords?

I must admit, at this point I nerd-sniped myself and actually didn’t play the text-adventure… I wanted to know how this works.

So I divided this problem into two sub-problems:

1. Defining keywords that can be accessed within the console
2. Calling functionality without adding the function invocation brackets () to our keywords.

1 Defining keywords that can be accessed within the console

This one is basically a solved problem. As soon as we put something into the global scope (in the browser this is also the window object), it will be accessible within the console. In other words:

function yes() {
  alert("Ready Player One");
}

would already allow us to put

> yes()

into the console and it opens the dialog box.

2 Calling functionality without invocation syntax

This one is trickier, but after having a look at Googles source-code, it turns out they are using a little trick by abusing getter functionality.

Sometimes, it is desirable to allow access to a property that returns a dynamically computed value, or you may want to reflect the status of an internal variable without requiring the use of explicit method calls. In JavaScript, this can be accomplished with the use of a getter. ¹

This means the getter is just a function that gets called when we access a property of something. At the same time accessing a property, doesn’t require function invocation syntax!

So I can define a getter for the yes keyword on the global window object so it can be used in the javascript console.

Object.defineProperty(window, "yes", {
  get() {
    alert("Ready Player One");
  },
});

Success! Now I can call yes within the console without invocation syntax