javascript里的+new Date写法
一直不会，今天看到了，大牛亚利告诉我的：
http://interglacial.com/javascript_spec/a-11.html
里说：
The unary + operator converts its operand to Number type.
The production UnaryExpression : + UnaryExpression is evaluated as follows:
一直不会，今天看到了，大牛亚利告诉我的：
http://interglacial.com/javascript_spec/a-11.html
里说：
The unary + operator converts its operand to Number type.
The production UnaryExpression : + UnaryExpression is evaluated as follows:
