Dot.js

 constrain() {
  if (this.pos.x > CANVAS_WIDTH - this.radius) {
    this.pos.x = CANVAS_WIDTH - this.radius;
  }
  if (this.pos.x < this.radius) {
    this.pos.x = this.radius;
  }
  if (this.pos.y > CANVAS_HEIGHT - this.radius) {
    this.pos.y = CANVAS_HEIGHT - this.radius;
  }
  if (this.pos.y < this.radius) {
    this.pos.y = this.radius;
  }
};