​

var walk;

​

function setup() {

  createCanvas(400, 400);

  walk = new Walker();

  fill(0, 200, 0);

  stroke(200,0,0);

  background(200,200,0);

}

​

function draw() {

  walk.step();

}

​

function Walker() {

  this.x = 200;

  this.y = 200;

​

  this.step = function() {

    var choice = int(random(0, 4));

    if      (choice == 0) this.x++;

    else if (choice == 1) this.x--;

    else if (choice == 2) this.y++;

    else if (choice == 3) this.y--;

    if ( this.x < 0 )     this.x = 0;

    if ( this.y < 0 )     this.y = 0;

    if ( this.x > width ) this.x = width;

    if ( this.y > height) this.y = height;

    // or use constrain() //  https://p5js.org/reference/#/p5/constrain

    //print('choice= ' + choice);

    ellipse(this.x, this.y, 4, 4);

  }

}