If, Else If, Else

sketch.js

var x;
var y;
var xSpeed;
var ySpeed;

function setup() {
	createCanvas(windowWidth, windowHeight);
	x = width/2;
	y =	height/2;
	xSpeed = 0;
	ySpeed = 0;
}

function draw() {
  noStroke();
  fill(255,0,0);
  ellipse(x, y, 10, 10);
  
  if (mouseX < width/2 && mouseY < height/2) {
    xSpeed = -1;
    ySpeed = -1;
  }
  else if(mouseX > width/2 && mouseY < height/2) {
    xSpeed = 1;
    ySpeed = -1;
  }
  else if(mouseX > width/2 && mouseY > height/2) {
    xSpeed = 1;
    ySpeed = 1;
  }
  else {
    xSpeed = -1;
    ySpeed = 1;
  }

  x = x + xSpeed;
  y = y + ySpeed;
}