how to check if a javascript object has an instance of a particular object

Question

say i have an array x and a constructor

function Road(footpath,divider,length,lanes){}

and

x[1] = new Road(1,1,1,1);

now how do i determine that x[1] is an object of type Road?

Answer 1

Simple like this

if(x[1] instanceof Road) {
    //Hey, you have a road!
}