举个例子：在一个项目的主程序server.js中引入mongoose模块，又在另一个文件use.js中给mongoose定义格式和自定义方法，最后在sever.js引入这个文件，可在use.js为什么又要引入mongoose模块，主程序server.js中不是以及经引入了么？求大佬告知，
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The use module is only referenced by the server, but mongoose is required in use. It is not defined and still needs to be introduced. http://www.infoq.com/cn/articles/nodejs-module-mechanism
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The use module is only referenced by the server, but mongoose is required in use. It is not defined and still needs to be introduced.
http://www.infoq.com/cn/articles/nodejs-module-mechanism