As an AI language model, I can provide you with a basic example of how you can create a simple text-based game using JavaScript and enclose it in script tags within a single HTML file. Since GTA 6 is not released yet, I'll provide a different example. Here's a simple number guessing game where the player has to guess a random number:
This simple game generates a random number between 1 and 100 and prompts the player to enter their guess using an input field. It then checks the guess against the random number and displays a message indicating whether the guess was too low, too high, or correct. The game starts when the page is loaded, and the player can continue guessing until they guess the correct number.
Please note that this is just a basic example, and you can further enhance and customize the game based on your requirements and desired gameplay mechanics.