draw function not looping as expected

I'm a beginner on here, so apologies in advance for naivety. I've made a simple image on Brackets using Javascript, trying to generate circles with random x and y values, and random colours. There are no issues showing when I open the browser console in Developer Tools, and when I save and refresh, it works. But I was expecting the refresh to happen on a loop through the draw function. Any clues as to where I've gone wrong?

Thanks so much

var r_x
var r_y
var r_width
var r_height
var x
var y
var z


function setup() 
{
    r_x = random()*500;
    r_y = random()*500;
    r_width = random()*200;
    r_height = r_width;
    x = random(1,255);
    y= random(1,255);
    z= random(1,255);

    createCanvas(512,512);
    background(255);

}

function draw()
{

    ellipse(r_x, r_y, r_width, r_height);
    fill(x, y, z);
}