grunt错误——Fatal error: Unable to find Gruntfile

E:\website\jquery-plugins>grunt
A valid Gruntfile could not be found. Please see the getting started guide for
more information on how to configure grunt: http://gruntjs.com/getting-started
Fatal error: Unable to find Gruntfile.

错误提示Gruntfile.js文件找不到，但项目中已经有Gruntfile.js文件，后来发现是用npm安装grunt模块时，没有安装完整（可能是中途中断了安装，但grunt模块的目录已经存在与node_modules目录下），解决办法是重新安装grunt模块:

E:\website\jquery-plugins>npm install grunt

再次执行:

E:\website\jquery-plugins> grunt
Loading "uglify.js" tasks...ERROR
>> Error: ENOENT, no such file or directory ‘E:\website\jquery-plugins\node_modules\grunt-contrib-uglify\node_modules\uglify-js\lib\utils.src‘
Warning: Task "uglify" not found. Use --force to continue.

Aborted due to warnings.

错误提示没有这个文件或者目录，猜测grunt的uglify插件也没有安装完整，重新安装：

E:\website\jquery-plugins>npm install grunt-contrib-uglify --save-dev

执行grunt的默认tasks（我这里的默认tasks只有uglify）

E:\website\jquery-plugins>grunt
Running "uglify:build" (uglify) task
>> 1 file created.

Done, without errors.