When the function is called every time the browser passed into two implicit parameters:
This 1. Function context object
2. Package argument object arguments
an array of arguments is a class object that may be used to manipulate data index, may acquire the length of the
When calling the function, we passed arguments will be saved in the arguments
arguments.length arguments can be used to obtain the length of
Even if we do not define shape parameters, arguments may be used by the arguments
arguments [0] represents an argument
arguments.callee 属性，
This property corresponds to a function object is currently executing function object
