What I learned on this mini-project.

Here, the click event is important in determining the outcome of the game, therefore we need to protect from falsely initiating them via scripts or other modifications.

Using the isTrusted property allows you to ensure the event was generated by a user action.

if (!event.isTrusted) return; // cheater

The code above, will return from the code block, if the event was not a result of user action.

This technique was used to prevent the same hole from being used twice in a row. It's important to return the value in the randomHole method, so that it can be used recursively.

let lastHole;

function randomHole(holes) {
    const idx = Math.floor(Math.random() * holes.length);
    const hole = holes[idx];

    if (lastHole === hole) {
        return randomHole(holes);
    }

    lastHole = hole;
    return hole;
}

Here, the lastHole variable will be assigned the randomly generated hole, if the following call generates the same hole, the randomHole will be çalled again until lastHole doesn't equal hole.