circle-vs-circle.js

var sth1 = {}, sth2 = {};

sth1.x = 10; // x pos
sth1.y = 10; // y pos
sth1.r = 10; // radius

sth2.x = 15; // x pos
sth2.y = 15; // y pos
sth2.r = 10; // radius

function testCircleCollision(obj1, obj2) {
	var dist = Math.sqrt( Math.pow(obj2.x - obj1.x, 2) + Math.pow(obj2.y - obj1.y, 2) );
	return dist < (obj1.r + obj2.r);
}

testCircleCollision(sth1, sth2);