​

​

let y = 50;

​

function setup() {

  createCanvas(100, 100);

​

  background(200);

​

  describe(

    'A gray square with a black circle at its center. The circle moves when the user presses an arrow key. It leaves a trail as it moves.'

  );

}

​

function draw() {

  // Update x and y if an arrow key is pressed.

  if (keyIsPressed === true) {

    if (keyCode === UP_ARROW) {

      y -= 1;

    } else if (keyCode === DOWN_ARROW) {

      y += 1;

    } else if (keyCode === LEFT_ARROW) {

      x -= 1;

    } else if (keyCode === RIGHT_ARROW) {

      x += 1;

    }

  }

​

  // Style the circle.

  fill(0);

​

  // Draw the circle at (x, y).

  circle(x, y, 5);

}