JavaScript Question of the Day March 18, 2025

The following code creates two circles that start on the left and right side of the canvas and move towards each other in the middle of the canvas:

let leftCircle;
let rightCircle;
let dx = 5;
const RADIUS = 30;

function main() {
    leftCircle = new Circle(RADIUS);
    leftCircle.setPosition(RADIUS, getHeight() / 2);
    leftCircle.setColor("blue");
    add(leftCircle);

    rightCircle = new Circle(RADIUS);
    rightCircle.setPosition(getWidth() - RADIUS, getHeight() / 2);
    rightCircle.setColor("red");
    add(rightCircle);

    setTimer(draw, 50);
}

function draw() {
    crashCheck(); // choose the correct version of this function
    leftCircle.move(dx, 0);
    rightCircle.move(-dx, 0);
}

main();

What would be the correct implementation of the crashCheck function if we wanted the circles to move in the opposite direction once they collide?

1. Correct Answer
   Incorrect Answer
   a

   function crashCheck() {
       if (leftCircle.getX() + RADIUS == rightCircle.getX() - RADIUS) {
           dx = -dx;
       }
   }

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2. Correct Answer
   Incorrect Answer
   b

   function crashCheck() {
       if (leftCircle.getX() - RADIUS == rightCircle.getX() + RADIUS) {
           dx = -dx;
       }
   }

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3. Correct Answer
   Incorrect Answer
   c

   function crashCheck() {
       if (leftCircle.getX() == rightCircle.getX() - RADIUS) {
           dx = -dx;
       }
   }

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4. Correct Answer
   Incorrect Answer
   d

   function crashCheck() {
       if (leftCircle.getX() == rightCircle.getX() + RADIUS) {
           dx = -dx;
       }
   }

   JavaScript