移植代码，因为用了get，set函数，子类又有重写get，set 的需求，子类的get，set 又无法调用父类的get，set，所以用了es6，发现发布的项目的时候会报错，

Files\LayaAirIDE\resources\app\node_modules\uglify-js\lib\parse.js:204
throw new JS_Parse_Error(message, line, col, pos);
^
Error

 at new JS_Parse_Error (E:\Program Files\LayaAirIDE\resources\app\node_modules\uglify-js\lib\parse.js:196:18)
 at js_error (E:\Program Files\LayaAirIDE\resources\app\node_modules\uglify-js\lib\parse.js:204:11)
 at croak (E:\Program Files\LayaAirIDE\resources\app\node_modules\uglify-js\lib\parse.js:663:9)
 at token_error (E:\Program Files\LayaAirIDE\resources\app\node_modules\uglify-js\lib\parse.js:671:9)
 at unexpected (E:\Program Files\LayaAirIDE\resources\app\node_modules\uglify-js\lib\parse.js:677:9)
 at semicolon (E:\Program Files\LayaAirIDE\resources\app\node_modules\uglify-js\lib\parse.js:697:43)
 at simple_statement (E:\Program Files\LayaAirIDE\resources\app\node_modules\uglify-js\lib\parse.js:871:73)

at E:\Program Files\LayaAirIDE\resources\app\node_