p5.js Old frames not deleting

Question

Using a javascript framework called p5, I'm trying to animate a circle that moves across the screen, however old frames don't delete, and this causes a line to show across the canvas.

var xPos = 0;

function setup() {
    createCanvas(400, 200)
    background(123);
}

function draw() {
    ellipse(xPos, height/2, 30, 30); //Draws the circle
    fill(255);
    xPos++; //Moves the circle a pixel over
    if(xPos > width){xPos = 0;} //resets the circle when it reaches the edge of the canvas
}

<script src="http://cdnjs.cloudflare.com/ajax/libs/p5.js/0.5.5/p5.js"></script>

Answer 1

That's because you only call the background() function once, right at the beginning of the program.

Then every time the draw() function is called, you draw another circle- without clearing out any old frames.

If you want to clear out old frames every frame, call the background() function at the beginning of your draw() function.