修改内置属性name

function foo() { }
var oldName = foo.name;
foo.name = "bar";
[oldName, foo.name]  ==>  ["foo", "foo"]

function foo() { }
Object.defineProperty(foo,"name",{writable:true})//修改内置属性name
var oldName = foo.name;
foo.name = "bar";
[oldName, foo.name] ==> ["foo", "bar"]