If statements with an extra variable

The code:

var speed = 3;


function setup() {
  createCanvas(400, 400);
  background(220);
}

function draw() {
  //background(220);
  
  fill(255, 0, 0)
  stroke('black')
  ellipse(mouseX, 200, 50, 50)
  mouseX = mouseX + speed
  
  if(mouseX > width){
    speed = -3
  }
  
  if(mouseX < 0){
    speed = 10
  }
  
}