x1 : hello
x1 : hello
x1 : hello
x1 : 0
o.x1 : hello
x2 : undefined
x2 : undefined
x2 : undefined
x2 : 0
o.x2 : undefined
x2 : world
x2 : world
x2 : 0
o.x2 : world
after apply
undefined
undefined
after apply
undefined
undefined