How do the objects?

var a = "t";
var b = {};
a = b;
a.x = 7;
b.y = "m";
a.y = b.x;
b.x = "p";

console.log(a);
console.log(b);

Tell me on what basis the assignment. Don't understand why the output in x is 'p' in both objects, and y the number 7, also in both sites.