Are 2 circles colliding

// circle objects: { x:, y:, radius: }
// return true if the 2 circles are colliding
// c1 and c2 are circles as defined above

function CirclesColliding(c1,c2){
    var dx=c2.x-c1.x;
    var dy=c2.y-c1.y;
    var rSum=c1.radius+c2.radius;
    return(dx*dx+dy*dy<=rSum*rSum);
}