sketchDownload
function setup() {
    createCanvas(200, 200);
    background(220);
    text("p5.js vers 0.9.0 test.", 10, 15);
}

function draw() {
	background(204);
	ellipse(50, 50, 80, 80);
}
sketchDownload
function setup() {
    createCanvas(300, 300);
    background(220);
//    text("p5.js vers 0.9.0 test.", 10, 15);
}

function draw() {
	if (mouseX < width / 2) {    // left side
		if (mouseY < height / 2) {     // top half
			background(255, 0, 0);
		}
		else {   // bottom half
			background(0, 255, 0);
		}
	}
	else {   // right side
		if (mouseY < height / 2) {  // top half
			background(0, 0, 255);
		}
		else {	// bottom half
			background(0, 0, 0);
		}
	}
}

Test Post

Here is a simple program.

sketchDownload
function setup() {
    createCanvas(300, 300);
    background(220);
//    text("p5.js vers 0.9.0 test.", 10, 15);
}

function draw() {
	if (mouseX < width / 2) {    // left side
		if (mouseY < height / 2) {     // top half
			background(255, 0, 0);
		}
		else {   // bottom half
			background(0, 255, 0);
		}
	}
	else {   // right side
		if (mouseY < height / 2) {  // top half
			background(0, 0, 255);
		}
		else {	// bottom half
			background(0, 0, 0);
		}
	}
}