var circle1 = {radius: 20, x: 5, y: 5}
var circle2 = {radius: 12, x: 10, y: 5}

var dx = circle1.x - circle2.x
var dy = circle1.y - circle2.y
var distance = Math.sqrt(dx * dx + dy * dy)

if (distance < circle1.radius + circle2.radius)
// collision detected!