Spawn enemy in game.js

game.js

 // Setup event listeners
    function setupEvents() {
      // Add event listeners for different types of events in the game
      // code omitted for brevity
    }
    
    // Spawn enemy
    function spawnEnemy(){
      var enemy = new Enemy();
      assets.push(enemy)
    }

    // Startup the game
    function init(){
      setupEvents();
      spawnEnemy();
    }