obj1.valueOf
obj1 is 1
obj1.valueOf
11
obj2.valueOf
obj2 is 2
obj2.valueOf
24
obj1.valueOf
obj2.valueOf
3
obj3.toString
world12
obj3.toString
hello world
obj1.valueOf
obj3.toString
1world
obj2.valueOf
obj3.toString
2world
obj3.toString
obj3.toString
worldworld