We create one file for each type of enemy. They are enemy.js, enemy-dummy.js, enemy1.js, enemy2.js, enemy3.js, and boss.js. Let's create these files and put them inside the scripts/board-objects/enemies/ folder. Then, we include them in the game's HTML. The base enemy.js file comes first because all the other enemy types are based on enemy.js and need its reference:

<script src="scripts/board-objects/enemies/enemy.js"></script>
<script src="scripts/board-objects/enemies/enemy-dummy.js"></script>
<script src="scripts/board-objects/enemies/enemy1.js"></script>
<script src="scripts/board-objects/enemies/enemy2.js"></script>
<script src="scripts/board-objects/enemies/enemy3.js"></script>
<script src="scripts/board-objects/enemies/boss.js"></script>

We need one more helper function. The removeItem function finds the given target in the given...