var radian = Math.atan2(mouseX - x, mouseY - y); // радианный угол
var rotate = (radian * (180 / Math.PI) * -1) + 90; // Переводим в градусы
var x = object.x + (object.width / 2);
var y = object.y + (object.height / 2);
function foo(name, surname, age) {
if (typeof surname == "number") {
age = surname;
surname = undefined;
}
// ...
}
foo("Ivan", "Ivanov", 23);
foo("Ivan", 23);