var ycor = 30;

var wt = 80;

var ht = 60;

​

function setup() {

  createCanvas(240, 120);

}

​

function draw() {

  background(220);

  if ((mouseX > xcor) && (mouseX < xcor + wt) && 

      (mouseY > ycor) && (mouseY < ycor + ht)) {

    fill(0);

  } else {

    fill(255);

  }

  rect(xcor, ycor, wt, ht);

}