array.find() is it working?

Hi, I am trying to do this array find tutorial to snapchat but it gives me error when I apply it to my project. I copy the exact tutorial but it gives error, here is my code

// -----JS CODE-----
var x = [
{
obj: "john",
pos: new vec3(0,0,0)
},
{
obj: "doe",
pos: new vec3(0,1,0)
}
];

function findPos(person){
return person.obj === "doe"
}

var a = x.find(findPos).pos
print(a)

Thanks for your help