let a=0;
function setup() {
createCanvas(600, 600);
background(0);
}
function draw() {
a+=0.1;
translate(mouseX,mouseY);
rotate(a);
scale(map(mouseX,0,600,0,1));
rect(50, 50, 50, 50);
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/1.1.9/p5.min.js"></script>