let y = 200;

let directions = [0, 1, 2, 3];

let direction;

let travel = 2;

function setup() {

  createCanvas(400, 400);

  background(42);

}

​

function draw() {

  strokeWeight(2);

  point(x, y);

​

  direction = random(directions);

  stroke(255);

  switch (direction) {

    case 0:

      x += travel;

      break;

    case 1:

      x -= travel;

      break;

    case 2:

      y += travel;

      break;

    case 3:

      y -= travel;

      break;

  }

}

​